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The current state of the problem of double-barred galaxies investigation is reviewed. The necessity for application of the panoramic spectroscopy methods to a detailed study of kinematics of these objects is being proved. The first results of observing double-barred galaxies at the 6m telescope using the multipupil spectrograph MPFS and the scanning interferometer Fabry-Perot are described.

The current state of the problem of double-barred galaxies investigation is reviewed. The necessity for application of the panoramic spectroscopy methods to a detailed study of kinematics of these objects is being proved. The first results of observing double-barred galaxies at the 6m telescope using the multipupil spectrograph MPFS and the scanning interferometer Fabry-Perot are described.

We present Spitzer IRAC $3.6-8 \mu$m and MIPS $24 \mu$m point-source catalogs for M $31$ and $15$ other mostly large, star forming galaxies at distances $\sim3.5-14$ Mpc including M $51$, M $83$, M $101$ and NGC $6946$. These catalogs contain $\sim1$ million sources including $\sim859,000$ in M 31 and $\sim116,000$ in the other galaxies. They were created following the procedures described in Khan et al. (2015) through a combination of point spread function (PSF) fitting and aperture photometry. These data products constitute a resource to improve our understanding of the IR-bright ($3.6-24 \mu$m) point-source populations in crowded extragalactic stellar fields and to plan observations with the James Webb Space Telescope.

We present Spitzer IRAC $3.6-8 \mu$m and MIPS $24 \mu$m point-source catalogs for M $31$ and $15$ other mostly large, star forming galaxies at distances $\sim3.5-14$ Mpc including M $51$, M $83$, M $101$ and NGC $6946$. These catalogs contain $\sim1$ million sources including $\sim859,000$ in M 31 and $\sim116,000$ in the other galaxies. They were created following the procedures described in Khan et al. (2015) through a combination of point spread function (PSF) fitting and aperture photometry. These data products constitute a resource to improve our understanding of the IR-bright ($3.6-24 \mu$m) point-source populations in crowded extragalactic stellar fields and to plan observations with the James Webb Space Telescope.

We present Spitzer IRAC $3.6-8 \mu$m and MIPS $24 \mu$m point-source catalogs for M $31$ and $15$ other mostly large, star forming galaxies at distances $\sim3.5-14$ Mpc including M $51$, M $83$, M $101$ and NGC $6946$. These catalogs contain $\sim1$ million sources including $\sim859,000$ in M 31 and $\sim116,000$ in the other galaxies. They were created following the procedures described in Khan et al. (2015) through a combination of point spread function (PSF) fitting and aperture photometry. These data products constitute a resource to improve our understanding of the IR-bright ($3.6-24 \mu$m) point-source populations in crowded extragalactic stellar fields and to plan observations with the James Webb Space Telescope.

We investigate the time evolution of dust properties, molecular hydrogen (H_2) contents, and star formation histories in galaxies by using our original chemodynamical simulations. The simulations include the formation of dust in the stellar winds of supernovae (SNe) and asymptotic giant branch (AGB) stars, the growth and destruction processes of dust in the interstellar medium (ISM), the formation of polycyclic aromatic hydrocarbon (PAH) dust in carbon-rich AGB stars, the H_2 formation on dust grains, and the H_2 photo-dissociation due to far ultra-violet (FUV) light in a self-consistent manner. We focus mainly on disk galaxies with different total masses in this preliminary study. The principle results are as follows: The star formation histories of disk galaxies can be regulated by the time evolution of interstellar dust, mainly because the formation rates of H_2 can be controlled by dust properties. The observed correlation between dust-to-gas-ratios (D) and gas-phase oxygen abundances (A_O = 12+log(O/H)) can be reproduced reasonably well in the present models. The disks show negative radial gradients (i.e., larger in inner regions) of H_2 fraction (f_H2), PAH-to-dust mass ratio (f_PAH), D, and A_O and these gradients evolve with time. The surface-mass densities of dust (Sigma_dust) are correlated more strongly with the total surface gas densities than with those of H_2. Local gaseous regions with higher D are more likely to have higher f_H2 in individual disks and total H_2 masses correlate well with total dust masses. More massive disk galaxies are more likely to have higher D, f_PAH, and f_H2 and smaller dust-to-stellar mass ratios. We also compare between galactic star formation histories in the metallicity-dependent and dust-dependent star formation models and find no major differences.

{The selection of AGB C and M stars from NIR colours has been done in recent years using adjustable criteria that are in needs of standardization if one wants to compare, in a coherent manner, properties of various populations.} We intend to assess the NIR colour technique to identify C and M stars. We compare the NIR colours of several C stars previously identified from spectroscopy or narrow band techniques in WLM, IC 10 and NGC 6822. We demonstrate that very few M stars have $(J-K)_0 > 1.4$ but a non negligible number of C stars are bluer than this limit. Thus, counts of M and C stars based on such limit do not produce pure samples. C/M ratios determined from NIR colours must be regarded as underestimates mainly because the M numbers include many warm C stars and also K stars if no blue limit is considered.

Scan of book Galaxies, stars and planets S177 Science Shart Module by Simon Clark, Simon Green and Stephen Serjeant [2012] {523.8--oclc}

We present photometric and spectroscopic observations of two luminous blue variable (LBV) stars in two extremely metal-deficient blue compact dwarf (BCD) galaxies, DDO 68 with 12+logO/H = 7.15 and PHL 293B with 12+logO/H = 7.72. These two BCDs are the lowest-metallicity galaxies where LBV stars have been detected, allowing to study the LBV phenomenon in the extremely low metallicity regime, and shedding light of the evolution of the first generation of massive stars born from primordial gas. We find that the strong outburst of the LBV star in DDO 68 occurred sometime between February 2007 and January 2008. We have compared the properties of the broad line emission in low-metallicity LBVs with those in higher metallicity LBVs. We find that, for the LBV star in DDO 68, broad emission with a P Cygni profile is seen in both H and He I emission lines. On the other hand, for the LBV star in PHL 293B, P Cygni profiles are detected only in H lines. For both LBVs, no heavy element emission line such as Fe II was detected. The Halpha luminosities of LBV stars in both galaxies are comparable to the one obtained for the LBV star in NGC 2363 (Mrk 71) which has a higher metallicity 12+logO/H = 7.89. On the other hand, the terminal velocities of the stellar winds in both low-metallicity LBVs are high, ~800 km/s, a factor of ~4 higher than the terminal velocities of the winds in high-metallicity LBVs. This suggests that stellar winds at low metallicity are driven by a different mechanism than the one operating in high-metallicity winds.

We present photometric and spectroscopic observations of two luminous blue variable (LBV) stars in two extremely metal-deficient blue compact dwarf (BCD) galaxies, DDO 68 with 12+logO/H = 7.15 and PHL 293B with 12+logO/H = 7.72. These two BCDs are the lowest-metallicity galaxies where LBV stars have been detected, allowing to study the LBV phenomenon in the extremely low metallicity regime, and shedding light of the evolution of the first generation of massive stars born from primordial gas. We find that the strong outburst of the LBV star in DDO 68 occurred sometime between February 2007 and January 2008. We have compared the properties of the broad line emission in low-metallicity LBVs with those in higher metallicity LBVs. We find that, for the LBV star in DDO 68, broad emission with a P Cygni profile is seen in both H and He I emission lines. On the other hand, for the LBV star in PHL 293B, P Cygni profiles are detected only in H lines. For both LBVs, no heavy element emission line such as Fe II was detected. The Halpha luminosities of LBV stars in both galaxies are comparable to the one obtained for the LBV star in NGC 2363 (Mrk 71) which has a higher metallicity 12+logO/H = 7.89. On the other hand, the terminal velocities of the stellar winds in both low-metallicity LBVs are high, ~800 km/s, a factor of ~4 higher than the terminal velocities of the winds in high-metallicity LBVs. This suggests that stellar winds at low metallicity are driven by a different mechanism than the one operating in high-metallicity winds.

We present photometric and spectroscopic observations of two luminous blue variable (LBV) stars in two extremely metal-deficient blue compact dwarf (BCD) galaxies, DDO 68 with 12+logO/H = 7.15 and PHL 293B with 12+logO/H = 7.72. These two BCDs are the lowest-metallicity galaxies where LBV stars have been detected, allowing to study the LBV phenomenon in the extremely low metallicity regime, and shedding light of the evolution of the first generation of massive stars born from primordial gas. We find that the strong outburst of the LBV star in DDO 68 occurred sometime between February 2007 and January 2008. We have compared the properties of the broad line emission in low-metallicity LBVs with those in higher metallicity LBVs. We find that, for the LBV star in DDO 68, broad emission with a P Cygni profile is seen in both H and He I emission lines. On the other hand, for the LBV star in PHL 293B, P Cygni profiles are detected only in H lines. For both LBVs, no heavy element emission line such as Fe II was detected. The Halpha luminosities of LBV stars in both galaxies are comparable to the one obtained for the LBV star in NGC 2363 (Mrk 71) which has a higher metallicity 12+logO/H = 7.89. On the other hand, the terminal velocities of the stellar winds in both low-metallicity LBVs are high, ~800 km/s, a factor of ~4 higher than the terminal velocities of the winds in high-metallicity LBVs. This suggests that stellar winds at low metallicity are driven by a different mechanism than the one operating in high-metallicity winds.

We present photometric and spectroscopic observations of two luminous blue variable (LBV) stars in two extremely metal-deficient blue compact dwarf (BCD) galaxies, DDO 68 with 12+logO/H = 7.15 and PHL 293B with 12+logO/H = 7.72. These two BCDs are the lowest-metallicity galaxies where LBV stars have been detected, allowing to study the LBV phenomenon in the extremely low metallicity regime, and shedding light of the evolution of the first generation of massive stars born from primordial gas. We find that the strong outburst of the LBV star in DDO 68 occurred sometime between February 2007 and January 2008. We have compared the properties of the broad line emission in low-metallicity LBVs with those in higher metallicity LBVs. We find that, for the LBV star in DDO 68, broad emission with a P Cygni profile is seen in both H and He I emission lines. On the other hand, for the LBV star in PHL 293B, P Cygni profiles are detected only in H lines. For both LBVs, no heavy element emission line such as Fe II was detected. The Halpha luminosities of LBV stars in both galaxies are comparable to the one obtained for the LBV star in NGC 2363 (Mrk 71) which has a higher metallicity 12+logO/H = 7.89. On the other hand, the terminal velocities of the stellar winds in both low-metallicity LBVs are high, ~800 km/s, a factor of ~4 higher than the terminal velocities of the winds in high-metallicity LBVs. This suggests that stellar winds at low metallicity are driven by a different mechanism than the one operating in high-metallicity winds.

We present photometric and spectroscopic observations of two luminous blue variable (LBV) stars in two extremely metal-deficient blue compact dwarf (BCD) galaxies, DDO 68 with 12+logO/H = 7.15 and PHL 293B with 12+logO/H = 7.72. These two BCDs are the lowest-metallicity galaxies where LBV stars have been detected, allowing to study the LBV phenomenon in the extremely low metallicity regime, and shedding light of the evolution of the first generation of massive stars born from primordial gas. We find that the strong outburst of the LBV star in DDO 68 occurred sometime between February 2007 and January 2008. We have compared the properties of the broad line emission in low-metallicity LBVs with those in higher metallicity LBVs. We find that, for the LBV star in DDO 68, broad emission with a P Cygni profile is seen in both H and He I emission lines. On the other hand, for the LBV star in PHL 293B, P Cygni profiles are detected only in H lines. For both LBVs, no heavy element emission line such as Fe II was detected. The Halpha luminosities of LBV stars in both galaxies are comparable to the one obtained for the LBV star in NGC 2363 (Mrk 71) which has a higher metallicity 12+logO/H = 7.89. On the other hand, the terminal velocities of the stellar winds in both low-metallicity LBVs are high, ~800 km/s, a factor of ~4 higher than the terminal velocities of the winds in high-metallicity LBVs. This suggests that stellar winds at low metallicity are driven by a different mechanism than the one operating in high-metallicity winds.

We present photometric and spectroscopic observations of two luminous blue variable (LBV) stars in two extremely metal-deficient blue compact dwarf (BCD) galaxies, DDO 68 with 12+logO/H = 7.15 and PHL 293B with 12+logO/H = 7.72. These two BCDs are the lowest-metallicity galaxies where LBV stars have been detected, allowing to study the LBV phenomenon in the extremely low metallicity regime, and shedding light of the evolution of the first generation of massive stars born from primordial gas. We find that the strong outburst of the LBV star in DDO 68 occurred sometime between February 2007 and January 2008. We have compared the properties of the broad line emission in low-metallicity LBVs with those in higher metallicity LBVs. We find that, for the LBV star in DDO 68, broad emission with a P Cygni profile is seen in both H and He I emission lines. On the other hand, for the LBV star in PHL 293B, P Cygni profiles are detected only in H lines. For both LBVs, no heavy element emission line such as Fe II was detected. The Halpha luminosities of LBV stars in both galaxies are comparable to the one obtained for the LBV star in NGC 2363 (Mrk 71) which has a higher metallicity 12+logO/H = 7.89. On the other hand, the terminal velocities of the stellar winds in both low-metallicity LBVs are high, ~800 km/s, a factor of ~4 higher than the terminal velocities of the winds in high-metallicity LBVs. This suggests that stellar winds at low metallicity are driven by a different mechanism than the one operating in high-metallicity winds.

stars and galaxies pdf

stars and galaxies pdf

Includes bibliography

Includes bibliographies

The stability of equilibrium configurations of galaxies or stars are time honored problems in astrophysics. We present mathematical results on these problems which have in recent years been obtained by Yan Guo and the author in the context of the Vlasov-Poisson and the Euler-Poisson model. Based on a careful analysis of the minimization properties of conserved quantities--the total energy and so-called Casimir functionals--non-linear stability results are obtained for a wide class of equilibria.

We combine a N-body simulation algorithm with a subgrid treatment of galaxy formation, mergers, and tidal destruction, and an observed conditional luminosity function Phi(L|M), to study the origin and evolution of galactic and extragalactic light inside a cosmological volume of size (100 Mpc)^3, in a concordance LCDM model. This algorithm simulates the growth of large-scale structures and the formation of clusters, the evolution of the galaxy population in clusters, the destruction of galaxies by mergers and tides, and the evolution of the intracluster light. We find that destruction of galaxies by mergers dominates over destruction by tides by about an order of magnitude at all redshifts. However, tidal destruction is sufficient to produce intracluster light fractions f_ICL that are sufficiently high to match observations. The bulk of the intracluster light (60%) is provided by intermediate galaxies of total masses 10^11 Msun-10^12 Msun and stellar masses 6x10^8 Msun-3x10^10 Msun that were tidally destroyed by even more massive galaxies. The contribution of low-mass galaxies to the intracluster light is small and the contribution of dwarf galaxies is negligible, even though, by numbers, most galaxies that are tidally destroyed are dwarfs. Tracking clusters back in time, we find that their values of f_ICL tend to increase over time, but can experience sudden changes that are sometimes non-monotonic. These changes occur during major mergers involving clusters of comparable masses but very different intracluster luminosities. Most of the tidal destruction events take place in the central regions of clusters. As a result, the intracluster light is more centrally concentrated than the galactic light. Our results support tidal destruction of intermediate-mass galaxies as a plausible scenario for the origin of the intracluster light.

(Abridged) We analyze the evolution of 42 spiral galaxies in the Spitzer Infrared Nearby Galaxies Survey, using extinction-corrected UV, optical and near-infrared radial profiles to probe the emission of stars of different ages as a function of radius. We fit these profiles with models that describe the chemical and spectro-photometric evolution of spiral disks within a self-consistent framework. These backward models succesfully reproduce the multi-wavelength profiles of our galaxies, except the UV profiles of some early-type disks. From the model fitting we infer the maximum circular velocity of the rotation curve (Vc) and the dimensionless spin parameter (lambda). The values of Vc are in good agreement with the velocities measured in HI rotation curves. While our sample is not volume-limited, the resulting distribution of spins is close to the lognormal function obtained in cosmological N-body simulations, peaking at ~0.03 regardless of the total halo mass. We do not find any evident trend between spin and Hubble type, besides an increase in the scatter for the latest types. According to the model, galaxies evolve along a roughly constant mass-size relation, increasing their scale-lengths as they become more massive. The radial scale-length of most disks in our sample seems to have increased at a rate of 0.05-0.06 kpc/Gyr, being now 20-25% larger than at z=1.

Great strides have been made in the last two decades in determining how galaxies evolve from their initial dark matter seeds to the complex structures we observe at z=0. The role of mergers has been documented through both observations and simulations, numerous satellites that may represent these initial dark matter seeds have been discovered in the Local Group, high redshift galaxies have been revealed with monstrous star formation rates, and the gaseous cosmic web has been mapped through absorption line experiments. Despite these efforts, the dark matter simulations that include baryons are still unable to accurately reproduce galaxies. One of the major problems is our incomplete understanding of how a galaxy accretes its baryons and subsequently forms stars. Galaxy formation simulations have been unable to accurately represent the required gas physics on cosmological timescales, and observations have only just begun to detect the star formation fuel over a range of redshifts and environments. How galaxies obtain gas and subsequently form stars is a major unsolved, yet tractable problem in contemporary extragalactic astrophysics. In this paper we outline how progress can be made in this area in the next decade.

We have used the Sloan Digital Sky Survey (SDSS) to undertake an investigation of lopsidedness in a sample of ~25,000 nearby galaxies (z < 0.06). We use the m=1 azimuthal Fourier mode between the 50% and 90% light radii as our measure of lopsidedness. The SDSS spectra are used to measure the properties of the stars, gas, and black hole in the central-most few-kpc-scale region. We show that there is a strong link between lopsidedness in the outer parts of the galactic disk and the youth of the stellar population in the central region. This link is independent of the other structural properties of the galaxy. These results provide a robust statistical characterization of the connections between accretion/interactions/mergers and the resulting star formation. We also show that residuals in the galaxy mass-metallicity relation correlate with lopsidedness (at fixed mass, the more metal-poor galaxies are more lopsided). This suggests that the events causing lopsidedness and enhanced star formation deliver lower metallicity gas into the galaxy's central region. Finally, we find that there is a trend for the more powerful active galactic nuclei to be hosted by more lopsided galaxies (at fixed galaxy mass, density, or concentration). However if we compare samples matched to have both the same structures and central stellar populations, we then find no difference in lopsidedness between active and non-active galaxies. This leads to the following picture. The presence of cold gas in the central region of a galaxy (irrespective of its origin) is essential for both star-formation and black hole growth. The delivery of cold gas is aided by the processes that produce lopsidedness. Other processes on scales smaller than we can probe with our data are required to transport the gas to the black hole.

We explore various instability models for the onset of star formation in irregular galaxies. Critical gas densities are calculated for gravitational instabilities with a thin, pure-gas disk, and with a thick disk composed of gas and a star-like fluid. We also calculated the stability properties of three dimensional systems including dark matter, considered the thermal state of the gas, and used a modified threshold column density written in terms of the local rate of shear instead of the epicyclic frequency. The model predictions were compared to the azimuthally-averaged present day star formation activity traced by the Halpha surface brightness, and to the 1 Gyr-integrated star formation activity represented by the stellar surface brightness. The ratio of the observed gas density to the critical gas density is lower by a factor of 2 in most of the Im galaxies than it is in spiral galaxies. Star formation ends before this ratio drops significantly in the outer regions, and it remains high in the inner regions where the ratio is often low. These results suggest that the critical gas density does not trace star formation with the same detail in irregular galaxies as it appears to trace it in giant spiral galaxies. The only azimuthally-averaged quantity that correlates with the current star formation activity in irregulars is the stellar surface density. Theoretical implications are discussed.

We explore various instability models for the onset of star formation in irregular galaxies. Critical gas densities are calculated for gravitational instabilities with a thin, pure-gas disk, and with a thick disk composed of gas and a star-like fluid. We also calculated the stability properties of three dimensional systems including dark matter, considered the thermal state of the gas, and used a modified threshold column density written in terms of the local rate of shear instead of the epicyclic frequency. The model predictions were compared to the azimuthally-averaged present day star formation activity traced by the Halpha surface brightness, and to the 1 Gyr-integrated star formation activity represented by the stellar surface brightness. The ratio of the observed gas density to the critical gas density is lower by a factor of 2 in most of the Im galaxies than it is in spiral galaxies. Star formation ends before this ratio drops significantly in the outer regions, and it remains high in the inner regions where the ratio is often low. These results suggest that the critical gas density does not trace star formation with the same detail in irregular galaxies as it appears to trace it in giant spiral galaxies. The only azimuthally-averaged quantity that correlates with the current star formation activity in irregulars is the stellar surface density. Theoretical implications are discussed.

We explore various instability models for the onset of star formation in irregular galaxies. Critical gas densities are calculated for gravitational instabilities with a thin, pure-gas disk, and with a thick disk composed of gas and a star-like fluid. We also calculated the stability properties of three dimensional systems including dark matter, considered the thermal state of the gas, and used a modified threshold column density written in terms of the local rate of shear instead of the epicyclic frequency. The model predictions were compared to the azimuthally-averaged present day star formation activity traced by the Halpha surface brightness, and to the 1 Gyr-integrated star formation activity represented by the stellar surface brightness. The ratio of the observed gas density to the critical gas density is lower by a factor of 2 in most of the Im galaxies than it is in spiral galaxies. Star formation ends before this ratio drops significantly in the outer regions, and it remains high in the inner regions where the ratio is often low. These results suggest that the critical gas density does not trace star formation with the same detail in irregular galaxies as it appears to trace it in giant spiral galaxies. The only azimuthally-averaged quantity that correlates with the current star formation activity in irregulars is the stellar surface density. Theoretical implications are discussed.

We identified and characterized the largest (536) RR Lyrae (RRL) sample in a Milky Way dSph satellite (Sculptor) based on optical photometry data collected over $\sim$24 years. The RRLs display a spread in V-magnitude ($\sim$0.35 mag) which appears larger than photometric errors and the horizontal branch (HB) luminosity evolution of a mono-metallic population. Using several calibrations of two different reddening free and metal independent Period-Wesenheit relations we provide a new distance estimate $\mu$=19.62 mag ($\sigma_{\mu}$=0.04 mag) that agrees well with literature estimates. We constrained the metallicity distribution of the old population, using the $M_I$ Period-Luminosity relation, and we found that it ranges from -2.3 to -1.5 dex. The current estimate is narrower than suggested by low and intermediate spectroscopy of RGBs ($\Delta$[Fe/H] $\le$ 1.5). We also investigated the HB morphology as a function of the galactocentric distance. The HB in the innermost regions is dominated by red HB stars and by RRLs, consistent with a more metal-rich population, while in the outermost regions it is dominated by blue HB stars and RRLs typical of a metal-poor population. Our results suggest that fast chemical evolution occurred in Sculptor, and that the radial gradients were in place at an early epoch.

A combination of evidence is presented suggesting that the majority of the stars in today's galaxies were born during a luminous infrared phase (LIRP) triggered by the local environment of galaxies. The CIRB is a fossil record of these LIRPs and therefore reflects the influence of triggered star formation through galaxy-galaxy interactions, including non merging tidal encounters. This scenario, in which galaxies experienced several LIRPs in their history, is consistent with the measured redshift evolution of the cosmic density of star formation rates and of stellar masses of galaxies.

A combination of evidence is presented suggesting that the majority of the stars in today's galaxies were born during a luminous infrared phase (LIRP) triggered by the local environment of galaxies. The CIRB is a fossil record of these LIRPs and therefore reflects the influence of triggered star formation through galaxy-galaxy interactions, including non merging tidal encounters. This scenario, in which galaxies experienced several LIRPs in their history, is consistent with the measured redshift evolution of the cosmic density of star formation rates and of stellar masses of galaxies.

In this paper we study the phenomenology of stars and galaxies in massive bigravity. We give parameter conditions for the existence of viable star solutions when the radius of the star is much smaller than the Compton wavelength of the graviton. If these parameter conditions are not met, we constrain the ratio between the coupling constants of the two metrics, in order to give viable conditions for e.g. neutron stars. For galaxies, we put constraints on both the Compton wavelength of the graviton and the conformal factor and coupling constants of the two metrics. The relationship between black holes and stars, and whether the former can be formed from the latter, is discussed. We argue that the different asymptotic structure of stars and black holes makes it unlikely that black holes form from the gravitational collapse of stars in massive bigravity.

In this paper we study the phenomenology of stars and galaxies in massive bigravity. We give parameter conditions for the existence of viable star solutions when the radius of the star is much smaller than the Compton wavelength of the graviton. If these parameter conditions are not met, we constrain the ratio between the coupling constants of the two metrics, in order to give viable conditions for e.g. neutron stars. For galaxies, we put constraints on both the Compton wavelength of the graviton and the conformal factor and coupling constants of the two metrics. The relationship between black holes and stars, and whether the former can be formed from the latter, is discussed. We argue that the different asymptotic structure of stars and black holes makes it unlikely that black holes form from the gravitational collapse of stars in massive bigravity.

In this paper we study the phenomenology of stars and galaxies in massive bigravity. We give parameter conditions for the existence of viable star solutions when the radius of the star is much smaller than the Compton wavelength of the graviton. If these parameter conditions are not met, we constrain the ratio between the coupling constants of the two metrics, in order to give viable conditions for e.g. neutron stars. For galaxies, we put constraints on both the Compton wavelength of the graviton and the conformal factor and coupling constants of the two metrics. The relationship between black holes and stars, and whether the former can be formed from the latter, is discussed. We argue that the different asymptotic structure of stars and black holes makes it unlikely that black holes form from the gravitational collapse of stars in massive bigravity.

We examine the global properties of the stellar and Hi components of 229 low H i mass dwarf galaxies extracted from the ALFALFA survey, including a complete sample of 176 galaxies with H i masses &lt;10(sup 7.7) solar mass and Hi line widths &lt;80 kilometers per second. Sloan Digital Sky Survey (SDSS) data are combined with photometric properties derived from Galaxy Evolution Explorer to derive stellar masses (M*) and star formation rates (SFRs) by fitting their UV-optical spectral energy distributions (SEDs). In optical images, many of the ALFALFA dwarfs are faint and of low surface brightness; only 56% of those within the SDSS footprint have a counterpart in the SDSS spectroscopic survey. A large fraction of the dwarfs have high specific star formation rates (SSFRs), and estimates of their SFRs and M* obtained by SED fitting are systematically smaller than ones derived via standard formulae assuming a constant SFR. The increased dispersion of the SSFR distribution at M* approximately less than10(exp 8)M(sub 0) is driven by a set of dwarf galaxies that have low gas fractions and SSFRs; some of these are dE/dSphs in the Virgo Cluster. The imposition of an upper Hi mass limit yields the selection of a sample with lower gas fractions for their M* than found for the overall ALFALFA population. Many of the ALFALFA dwarfs, particularly the Virgo members, have H i depletion timescales shorter than a Hubble time. An examination of the dwarf galaxies within the full ALFALFA population in the context of global star formation (SF) laws is consistent with the general assumptions that gas-rich galaxies have lower SF efficiencies than do optically selected populations and that Hi disks are more extended than stellar ones.

We examine possible phenomenological constraints for the joint evolution of supermassive black holes (SMBH) and their host spheroids. We compare all the available observational data on the redshift evolution of the total stellar mass and star formation rate density in the Universe with the mass and accretion rate density evolution of supermassive black holes, estimated from the hard X-ray selected luminosity function of quasars and active galactic nuclei (AGN) for a given radiative efficiency, \epsilon. We assume that the ratio of the stellar mass in spheroids to the black hole mass density evolves as (1+z)^{-\alpha}, while the ratio of the stellar mass in disks+irregulars to that in spheroids evolves as (1+z)^{-\beta}, and we derive constraints on \alpha, \beta and \epsilon. We find that \alpha>0 at the more than 4-sigma level, implying a larger black hole mass at higher redshift for a given spheroid stellar mass. The favored values for \beta are typically negative, suggesting that the fraction of stellar mass in spheroids decreases with increasing redshift. This is consistent with recent determinations that show that the mass density at high redshift is dominated by galaxies with irregular morphology. In agreement with earlier work, we constrain \epsilon to be between 0.04 and 0.11, depending on the exact value of the local SMBH mass density, but almost independently of \alpha and \beta.

Astrophysical jets are associated with the formation of young stars of all masses, stellar and massive black holes, and perhaps even with the formation of massive planets. Their role in the formation of planets, stars, and galaxies is increasingly appreciated and probably reflects a deep connection between the accretion flows - by which stars and black holes may be formed - and the efficiency by which magnetic torques can remove angular momentum from such flows. We compare the properties and physics of jets in both non-relativistic and relativistic systems and trace, by means of theoretical argument and numerical simulations, the physical connections between these different phenomena. We discuss the properties of jets from young stars and black holes, give some basic theoretical results that underpin the origin of jets in these systems, and then show results of recent simulations on jet production in collapsing star-forming cores as well as from jets around rotating Kerr black holes.

Astrophysical jets are associated with the formation of young stars of all masses, stellar and massive black holes, and perhaps even with the formation of massive planets. Their role in the formation of planets, stars, and galaxies is increasingly appreciated and probably reflects a deep connection between the accretion flows - by which stars and black holes may be formed - and the efficiency by which magnetic torques can remove angular momentum from such flows. We compare the properties and physics of jets in both non-relativistic and relativistic systems and trace, by means of theoretical argument and numerical simulations, the physical connections between these different phenomena. We discuss the properties of jets from young stars and black holes, give some basic theoretical results that underpin the origin of jets in these systems, and then show results of recent simulations on jet production in collapsing star-forming cores as well as from jets around rotating Kerr black holes.

Astrophysical jets are associated with the formation of young stars of all masses, stellar and massive black holes, and perhaps even with the formation of massive planets. Their role in the formation of planets, stars, and galaxies is increasingly appreciated and probably reflects a deep connection between the accretion flows - by which stars and black holes may be formed - and the efficiency by which magnetic torques can remove angular momentum from such flows. We compare the properties and physics of jets in both non-relativistic and relativistic systems and trace, by means of theoretical argument and numerical simulations, the physical connections between these different phenomena. We discuss the properties of jets from young stars and black holes, give some basic theoretical results that underpin the origin of jets in these systems, and then show results of recent simulations on jet production in collapsing star-forming cores as well as from jets around rotating Kerr black holes.

We present first results from an HST/ACS imaging survey of stars and star clusters in five nearby spiral galaxies. This contribution concentrates on NGC 1313, a highly distorted late-type barred spiral. We compare the field star and cluster formation histories in our three ACS pointings for this galaxy. In one pointing, both the cluster and field star age distributions show clear evidence for a ramp-up in the star formation rate about 100 Myrs ago.

We present first results from an HST/ACS imaging survey of stars and star clusters in five nearby spiral galaxies. This contribution concentrates on NGC 1313, a highly distorted late-type barred spiral. We compare the field star and cluster formation histories in our three ACS pointings for this galaxy. In one pointing, both the cluster and field star age distributions show clear evidence for a ramp-up in the star formation rate about 100 Myrs ago.

Semi-numeric methods have made it possible to efficiently model the epoch of reionisation (EoR). While most implementations involve a reduction to a simple three-parameter model, we introduce a new mass-dependent ionising efficiency parameter that folds in physical parameters that are constrained by the latest numerical simulations. This new parameterization enables the effective modeling of a broad range of host halo masses containing ionising sources, extending from the smallest Population III host halos with $M \sim 10^6 M_\odot$, which are often ignored, to the rarest cosmic peaks with $M \sim 10^{12} M_\odot$ during EoR. We compare the resulting ionising histories with a typical three-parameter model and also compare with the latest constraints from the Planck mission. Our model results in a optical depth due to Thomson scattering, $\tau_{\mathrm{e}}$ = 0.057, that is consistent with Planck. The largest difference in our model is shown in the resulting bubble size distributions which peak at lower characteristic sizes and are broadened. We also consider the uncertainties of the various physical parameters and comparing the resulting ionising histories broadly disfavors a small contribution from galaxies. As the smallest haloes cease a meaningful contribution to the ionising photon budget after $z = 10$, implying they play a role in determining the start of EoR and little else, an ionising photon escape fraction greater than 0.6 is also broadly disfavored.

We use 30 high-resolution dark matter halos of the $Caterpillar$ simulation suite to probe the first stars and galaxies of Milky Way-mass systems. We quantify the environment of the high-$z$ progenitors of the Milky Way and connect them to the properties of the host and satellites today. We identify the formation sites of the first generation of Population III (Pop III) stars ($z$ ~ 25) and first galaxies ($z$ ~ 22) with several different models based on a minimum halo mass including a simple model for Lyman-Werner feedback. Through this method we find approximately 23,000 $\pm$ 5,000 Pop III potentially star-forming sites per Milky Way-mass host, though this number is drastically reduced to ~550 star-forming sites when Lyman-Werner feedback is included, as it has critical effects at these length scales. The majority of these halos identified form in isolation (96% at $z$ = 15) and are not subject to external enrichment by neighboring halos (median separation ~1 pkpc at $z$ = 15), though half merge with a system larger than themselves within 1.5 Gyrs. Approximately 55% of the entire population has merged into the host halo by $z$ = 0. Using particle tagging, we additionally trace the Pop III remnant population to $z$ = 0 and find an order of magnitude scatter in their number density at small (i.e. r $ $ 50 kpc) galactocentric radii at $z$ = 0. Using our large number of realizations, we provide fitting functions for determining the number of progenitor minihalo and atomic cooling halo systems that present-day dwarf galaxies and the Magellanic cloud system might have accreted since their formation. We demonstrate that observed dwarf galaxies with stellar masses below 10$^{4.6}$ M$_{\odot}$ are unlikely to have merged with any other star-forming systems.

Large numbers of young stars are formed in merging galaxies, such as the Antennae galaxies. Most of these stars are formed in compact star clusters (i.e., super star clusters), which have been the focus of a large number of studies. However, an increasing number of projects are beginning to focus on the individual stars as well. In this contribution, we examine a few results relevant to the triggering of star and star cluster formation; ask what fraction of stars form in the field rather than in clusters; and begin to explore the demographics of both the massive stars and star clusters in the Antennae.

In systems undergoing starbursts the evolution of the young stellar population is expected to drive changes in the emission line properties. This evolution is usually studied theoretically, with a combination of evolutionary synthesis models for the spectral energy distribution of starbursts and photoionization calculations. In this paper we present a more empirical approach to this issue. We apply empirical population synthesis techniques to samples of Starburst and HII galaxies in order to measure their evolutionary state and correlate the results with their emission line properties. A couple of useful tools are introduced which greatly facilitate the interpretation of the synthesis: (1) an evolutionary diagram, whose axis are the strengths of the young, intermediate age and old components of the stellar population mix, and (2) the mean age of stars associated with the starburst, $\ov{t}_{SB}$. These tools are tested with grids of theoretical galaxy spectra and found to work very well even when only a small number of observed properties (absorption line equivalent widths and continuum colors) is used in the synthesis. Starburst nuclei and HII galaxies are found to lie on a well defined sequence in the evolutionary diagram. Using the empirically defined mean starburst age in conjunction with emission line data we have verified that the equivalent widths of H$\beta$ and [OIII] decrease for increasing $\ov{t}_{SB}$. The same evolutionary trend was identified for line ratios indicative of the gas excitation, although no clear trend was identified for metal rich systems. All these results are in excellent agreement with long known, but little tested, theoretical expectations.

Once the first sources have formed, their mass deposition, energy injection and emitted radiation can deeply affect the subsequent galaxy formation process and influence the evolution of the IGM via a number of so-called feedback effects. The word 'feedback' is by far one of the most used in modern cosmology, where it is applied to a vast range of situations and astrophysical objects. Generally speaking, the concept of feedback invokes a back reaction of a process on itself or on the causes that have produced it. The character of feedback can be either negative or positive. Here, I will review the present status of investigation of the feedback effects from the first stars and galaxies.

Stars generally form in aggregates, some of which are bound ('clusters') while others are unbound and disperse on short ($\sim10$ Myr) timescales ('associations'). The fraction of stars forming in bound clusters ($\Gamma$) is a fundamental outcome of the star formation process. Recent observational and theoretical work has suggested that $\Gamma$ increases with the gas surface density ($\Sigma$) or star formation rate (SFR) surface density ($\Sigma_{\rm SFR}$), both within galaxies and between different ones. However, a recent paper by Chandar et al. has challenged these results, showing that the $total$ number of stellar aggregates per unit SFR does not vary systematically with the host galaxy's absolute SFR. In this Letter, we show that no variations are expected when no distinction is made between bound and unbound aggregates, because the sum of these two fractions should be close to unity. We also demonstrate that any scaling of $\Gamma$ with the absolute SFR is much weaker than with $\Sigma_{\rm SFR}$, due to the mass-radius-SFR relation of star-forming 'main sequence' galaxies. The environmental variation of $\Gamma$ should therefore be probed as a function of area-normalised quantities, such as $\Sigma$ or $\Sigma_{\rm SFR}$. We present a set of guidelines for meaningful observational tests of cluster formation theories and show that these resolve the reported discrepancy.

Recent surveys have discovered hundreds of low surface brightness galaxies in the local (z < 0.1) Universe. Plots of the surface brightness distribution (the space density of galaxies plotted against central surface brightness) show a flat distribution from the bright-end cutoff of 21.65 through the current observational limit of 25.0 B mag arcsec^{-2}. As no trend is seen to indicate the size or mass of galaxies decreases with decreasing central surface brightness, it is likely that a significant percentage of the baryon content in the universe is contained in these diffuse systems. In this paper I briefly review the known properties of low surface brightness galaxies, and describe some current theories on the baryonic mass fraction of low surface brightness systems and their consequences.

We give two examples of spiral galaxies that show non-circular gas motions in the inner kiloparsecs, from SAURON integral field spectroscopy. We use harmonic decomposition of the velocity field of the ionized gas to study the underlying mass distribution, employing linear theory. The higher order harmonic terms and the main kinematic features of the observed data are consistent with an analytically constructed simple bar model. We also present maps of a number of strong absorption lines in M 100, derive simple stellar populations and correlate them with features in the gas kinematics.

We investigate the attenuation law seen through an interstellar medium (ISM) with clumpy spatial distributions of stars and dust. The clumpiness of the dust distribution is introduced by a multi-phase ISM model. We solve a set of radiative transfer equations with multiple anisotropic scatterings through the clumpy ISM in a 1-D plane-parallel geometry by using the mega-grain approximation, in which dusty clumps are regarded as very large particles (i.e. mega-grains). The clumpiness of the stellar distribution is introduced by the youngest stars embedded in the clumps. We assume a smooth spatial distribution for older stars. The youngest stars are surrounded by denser dusty gas and suffer stronger attenuation than diffuse older stars (i.e. age-selective attenuation). The apparent attenuation law is a composite of the attenuation laws for the clumpy younger stars and for the diffuse older stars with a luminosity weight. In general, the stellar population dominating the luminosity changes from older stars to younger stars as the wavelength decreases. This makes the attenuation law steep; the composite attenuation rapidly increases from small attenuation for older stars at a long wavelength to large attenuation for younger stars at a short wavelength. The resultant attenuation law of normal disc galaxies is expected to be much steeper than that of starburst galaxies observed by Calzetti et al. Finally, the Calzetti's attenuation law is regarded as a special case with a large density in our framework.

Stars and their kinematics provide one of the tools available for studies of the shapes of galaxies and their halos. In this review I focus on two specific applications: the shape of the Milky Way dark halo and the shape of the LMC disk. The former is constrained by a variety of observations, but an accurate determination of the axial ratio q_DH remains elusive. A very flattened Milky Way dark halo with q_DH < 0.4 is ruled out, and values q_DH > 0.7 appear most consistent with the data. Near-IR surveys have revealed that the LMC disk is not approximately circular, as long believed, but instead has an axial ratio of 0.7 in the disk plane. The elongation is perpendicular to the Magellanic Stream, indicating that it is most likely due to the tidal force of the Milky Way. Equilibrium dynamical modeling of galaxies is important for many applications. At the same time, detailed studies of tidal effects and tidal streams have the potential to improve our understanding of both the Milky Way dark halo and the structure of satellite galaxies such as the LMC.

A rotating continuum of particles attracted to each other by gravity may be modeled by the Euler-Poisson system. The existence of solutions is a very classical problem. Here it is proven that a curve of solutions exists, parametrized by the rotation speed, with a fixed mass independent of the speed. The rotation is allowed to vary with the distance to the axis. A special case is when the equation of state is $p=\rho^\gamma,\ 6/5