Population Of Spiral Galaxies Research Articles

Identification of Intermediate-mass Black Hole Candidates among a Sample of Sd Galaxies

We analyzed images of every northern hemisphere Sd galaxy listed in the Third Reference Catalogue of Bright Galaxies with a relatively face-on inclination (θ ≤ 30°). Specifically, we measured the spiral arms’ winding angle, ϕ, in 85 galaxies. We applied a novel black hole mass planar scaling relation involving the rotational velocities (from the literature) and pitch angles of each galaxy to predict central black hole masses. This yielded 23 galaxies, each having at least a 50% chance of hosting a central intermediate-mass black hole (IMBH), 102 < M • ≤ 105 M ☉. These 23 nearby (≲50 Mpc) targets may be suitable for an array of follow-up observations to check for active nuclei. Based on our full sample of 85 Sd galaxies, we estimate that the typical Sd galaxy (which tends to be bulgeless) harbors a black hole with log(M•/M☉)=6.00±0.14 , but with a 27.7% chance of hosting an IMBH, making this morphological type of galaxy fertile ground for hunting elusive IMBHs. Thus, we find that a ∼106 M ☉ black hole corresponds roughly to the onset of bulge development and serves as a conspicuous waypoint along the galaxy–supermassive black hole coevolution journey. Our survey suggests that >1.22% of bright galaxies (B T ≲ 15.5 mag) in the local Universe host an IMBH (i.e., the “occupation fraction”), which implies a number density >4.96 × 10−6 Mpc−3 for central IMBHs. Finally, we observe that Sd galaxies exhibit an unexpected diversity of properties that resemble the general population of spiral galaxies, albeit with an enhanced signature of the eponymous prototypical traits (i.e., low masses, loosely wound spiral arms, and smaller rotational velocities).

BUDDI-MaNGA

The many unique properties of galaxies are shaped by physical processes that affect different components of the galaxy – such as their bulges and discs – in different ways, and they leave characteristic imprints on the light and spectra of these components. Disentangling these spectra reveals vital clues that can be traced back in time to understand how galaxies, and their components, form and evolve throughout their lifetimes. With BUDDI, we have decomposed the integral field unit (IFU) datacubes in SDSS-MaNGA DR17 into Sérsic bulge and exponential disc components and extracted clean bulge and disc spectra. BUDDI-MaNGA is the first large statistical sample of such decomposed spectra of 1452 galaxies covering morphologies from ellipticals to late-type spirals. We derive stellar masses of the individual components with spectral energy distribution (SED) fitting using BAGPIPES and estimate their mean mass-weighted stellar metallicities and stellar ages using PPXF. With this information, we reconstruct the mass assembly histories of the bulges and discs of 968 spiral galaxies (Sa-Sm types). Our results show a clear downsizing effect especially for the bulges, with more massive components assembling earlier and faster than the less massive ones. Additionally, we compare the stellar populations of the bulges and discs in these galaxies, and find that a majority of the bulges host more metal-rich and older stars than their disc counterparts. Nevertheless, we also find a non-negligible fraction of the spiral galaxy population in our sample contains bulges that are younger and more metal-enhanced than their discs. We interpret these results, taking into account how their formation histories and current stellar populations depend on stellar mass and morphology.

The PHANGS-HST Survey: Physics at High Angular Resolution in Nearby Galaxies with the Hubble Space Telescope

Abstract The PHANGS program is building the first data set to enable the multiphase, multiscale study of star formation across the nearby spiral galaxy population. This effort is enabled by large survey programs with the Atacama Large Millimeter/submillimeter Array (ALMA), MUSE on the Very Large Telescope, and the Hubble Space Telescope (HST), with which we have obtained CO(2–1) imaging, optical spectroscopic mapping, and high-resolution UV–optical imaging, respectively. Here, we present PHANGS-HST, which has obtained NUV–U–B–V–I imaging of the disks of 38 spiral galaxies at distances of 4–23 Mpc, and parallel V- and I-band imaging of their halos, to provide a census of tens of thousands of compact star clusters and multiscale stellar associations. The combination of HST, ALMA, and VLT/MUSE observations will yield an unprecedented joint catalog of the observed and physical properties of ∼100,000 star clusters, associations, H ii regions, and molecular clouds. With these basic units of star formation, PHANGS will systematically chart the evolutionary cycling between gas and stars across a diversity of galactic environments found in nearby galaxies. We discuss the design of the PHANGS-HST survey and provide an overview of the HST data processing pipeline and first results. We highlight new methods for selecting star cluster candidates, morphological classification of candidates with convolutional neural networks, and identification of stellar associations over a range of physical scales with a watershed algorithm. We describe the cross-observatory imaging, catalogs, and software products to be released. The PHANGS high-level science products will seed a broad range of investigations, in particular, the study of embedded stellar populations and dust with the James Webb Space Telescope, for which a PHANGS Cycle 1 Treasury program to obtain eight-band 2–21 μm imaging has been approved.

Analysis of the Alignment of Non-Random Patterns of Spin Directions in Populations of Spiral Galaxies

Observations of non-random distribution of galaxies with opposite spin directions have recently attracted considerable attention. Here, a method for identifying cosine-dependence in a dataset of galaxies annotated by their spin directions is described in the light of different aspects that can impact the statistical analysis of the data. These aspects include the presence of duplicate objects in a dataset, errors in the galaxy annotation process, and non-random distribution of the asymmetry that does not necessarily form a dipole or quadrupole axes. The results show that duplicate objects in the dataset can artificially increase the likelihood of cosine dependence detected in the data, but a very high number of duplicate objects is required to lead to a false detection of an axis. Inaccuracy in galaxy annotations has relatively minor impact on the identification of cosine dependence when the error is randomly distributed between clockwise and counterclockwise galaxies. However, when the error is not random, even a small bias of 1% leads to a statistically significant cosine dependence that peaks at the celestial pole. Experiments with artificial datasets in which the distribution was not random showed strong cosine dependence even when the data did not form a full dipole axis alignment. The analysis when using the unmodified data shows asymmetry profile similar to the profile shown in multiple previous studies using several different telescopes.

Precision Scaling Relations for Disk Galaxies in the Local Universe

Abstract We build templates of rotation curves as a function of the I-band luminosity via the mass modeling (by the sum of a thin exponential disk and a cored halo profile) of suitably normalized, stacked data from wide samples of local spiral galaxies. We then exploit such templates to determine fundamental stellar and halo properties for a sample of about 550 local disk-dominated galaxies with high-quality measurements of the optical radius R opt and of the corresponding rotation velocity V opt. Specifically, we determine the stellar M ⋆ and halo M H masses, the halo size R H and velocity scale V H, and the specific angular momenta of the stellar j ⋆ and dark matter j H components. We derive global scaling relationships involving such stellar and halo properties both for the individual galaxies in our sample and for their mean within bins; the latter are found to be in pleasing agreement with previous determinations by independent methods (e.g., abundance matching techniques, weak-lensing observations, and individual rotation curve modeling). Remarkably, the size of our sample and the robustness of our statistical approach allow us to attain an unprecedented level of precision over an extended range of mass and velocity scales, with 1σ dispersion around the mean relationships of less than 0.1 dex. We thus set new standard local relationships that must be reproduced by detailed physical models, which offer a basis for improving the subgrid recipes in numerical simulations, that provide a benchmark to gauge independent observations and check for systematics, and that constitute a basic step toward the future exploitation of the spiral galaxy population as a cosmological probe.

Galaxy Zoo: constraining the origin of spiral arms

Since the discovery that the majority of low-redshift galaxies exhibit some level of spiral structure, a number of theories have been proposed as to why these patterns exist. A popular explanation is a process known as swing amplification, yet there is no observational evidence to prove that such a mechanism is at play. By using a number of measured properties of galaxies, and scaling relations where there are no direct measurements, we model samples of SDSS and S$^4$G spiral galaxies in terms of their relative halo, bulge and disc mass and size. Using these models, we test predictions of swing amplification theory with respect to directly measured spiral arm numbers from Galaxy Zoo 2. We find that neither a universal cored or cuspy inner dark matter profile can correctly predict observed numbers of arms in galaxies. However, by invoking a halo contraction/expansion model, a clear bimodality in the spiral galaxy population emerges. Approximately 40 per cent of unbarred spiral galaxies at $z \lesssim 0.1$ and $\mathrm{M_*} \gtrsim 10^{10} \mathrm{M_\odot}$ have spiral arms that can be modelled by swing amplification. This population display a significant correlation between predicted and observed spiral arm numbers, evidence that they are swing amplified modes. The remainder are dominated by two-arm systems for which the model predicts significantly higher arm numbers. These are likely driven by tidal interactions or other mechanisms.

Galactic magnetic fields and hierarchical galaxy formation

A framework is introduced for coupling the evolution of galactic magnetic fields sustained by the mean-field dynamo with the formation and evolution of galaxies in cold dark matter cosmology. Estimates of the steady-state strength of the large-scale and turbulent magnetic fields from mean-field and fluctuation dynamo models are used together with galaxy properties predicted by semi-analytic models of galaxy formation for a population of spiral galaxies. We find that the field strength is mostly controlled by the evolving gas content of the galaxies. Thus, because of the differences in the implementation of the star formation law, feedback from supernovae and ram-pressure stripping, each of the galaxy formation models considered predicts a distribution of field strengths with unique features. The most prominent of them is the difference in typical magnetic fields strengths obtained for the satellite and central galaxy populations as well as the typical strength of the large-scale magnetic field in galaxies of different mass.

The ATLAS 3D project – XXIV. The intrinsic shape distribution of early-type galaxies

We use the ATLAS3D sample to perform a study of the intrinsic shapes of early-type galaxies, taking advantage of the available combined photometric and kinematic data. Based on our ellipticity measurements from the Sloan Digital Sky Survey Data Release 7, and additional imaging from the Isaac Newton Telescope, we first invert the shape distribution of fast and slow rotators under the assumption of axisymmetry. The so-obtained intrinsic shape distribution for the fast rotators can be described with a Gaussian with a mean flattening of q = 0.25 and standard deviation σq = 0.14, and an additional tail towards rounder shapes. The slow rotators are much rounder, and are well described with a Gaussian with mean q = 0.63 and σq = 0.09. We then checked that our results were consistent when applying a different and independent method to obtain intrinsic shape distributions, by fitting the observed ellipticity distributions directly using Gaussian parametrizations for the intrinsic axis ratios. Although both fast and slow rotators are identified as early-type galaxies in morphological studies, and in many previous shape studies are therefore grouped together, their shape distributions are significantly different, hinting at different formation scenarios. The intrinsic shape distribution of the fast rotators shows similarities with the spiral galaxy population. Including the observed kinematic misalignment in our intrinsic shape study shows that the fast rotators are predominantly axisymmetric, with only very little room for triaxiality. For the slow rotators though there are very strong indications that they are (mildly) triaxial.

Stellar clusters in M83: formation, evolution, disruption and the influence of the environment

We study the stellar cluster population in two adjacent fields in the nearby, face-on spiral galaxy, M83, using WFC3/HST imaging. The clusters are selected through visual inspection to be centrally concentrated, symmetric, and resolved on the images, which allows us to differentiate between clusters and likely unbound associations. We compare our sample with previous studies and show that the differences between the catalogues are largely due to the inclusion of large numbers of diffuse associations within previous catalogues. The luminosity function of the clusters is well approximated by a power-law with index, -2, over most of the observed range, however a steepening is seen at M_V = -9.3 and -8.8 in the inner and outer fields, respectively. Additionally, we show that the cluster population is inconsistent with a pure power-law mass distribution, but instead exhibits a truncation at the high mass end. If described as a Schechter function, the characteristic mass is 1.6 and 0.5 * 10^5 Msun, for the inner and outer fields, respectively, in agreement with previous estimates of other cluster populations in spiral galaxies. Comparing the predictions of the mass independent disruption (MID) and mass dependent disruption (MDD) scenarios with the observed distributions, we find that both models can accurately fit the data. However, for the MID case, the fraction of clusters destroyed (or mass lost) per decade in age is dependent on the environment, hence, the age/mass distributions of clusters are not universal. In the MDD case, the disruption timescale scales with galactocentric distance (being longer in the outer regions of the galaxy) in agreement with analytic and numerical predictions. Finally, we discuss the implications of our results on other extragalactic surveys, focussing on the fraction of stars that form in clusters and the need (or lack thereof) for infant mortality.

The ATLAS3D project - V. The CO Tully-Fisher relation of early-type galaxies

We demonstrate here using both single-dish and interferometric observations that CO molecules are an excellent kinematic tracer, even in high-mass galaxies, allowing us to investigate for the first time the CO Tully-Fisher relation of early-type galaxies. We compare the Tully-Fisher relations produced using both single-dish and interferometric data and various inclination estimation methods, and evaluate the use of the velocity profile shape as a criterion for selecting galaxies in which the molecular gas extends beyond the peak of the rotation curve. We show that the gradient and zero-point of the best-fit relations are robust, independent of the velocity measure and inclination used, and agree with those of relations derived using stellar kinematics. We also show that the early-type CO Tully-Fisher (CO-TF) relation is offset from the CO-TF of spirals by 0.98 \pm 0.22 magnitude at Ks-band, in line with other results. The intrinsic scatter of the relation is found to be \approx 0.4 magnitudes, similar to the level found in the spiral galaxy population. Next generation facilities such as the Large Millimeter Telescope (LMT) and the Atacama Large Millimeter/Sub-millimeter Array (ALMA) should allow this technique to be used in higher-redshift systems, providing a simple new tool to trace the mass-to-light ratio evolution of the most massive galaxies over cosmic time.

BINARY COMPACT OBJECT COALESCENCE RATES: THE ROLE OF ELLIPTICAL GALAXIES

We estimate binary compact object merger detection rates for LIGO, including the binaries formed in ellipticals long ago. Specifically, we convolve hundreds of model realizations of elliptical- and spiral-galaxy population syntheses with a model for elliptical- and spiral-galaxy star formation history as a function of redshift. Our results favor local merger rate densities of 4\times 10^{-3} {Mpc}^{-3}{Myr}^{-1} for binary black holes (BH), 3\times 10^{-2} {Mpc}^{-3}{Myr}^{-1} for binary neutron stars (NS), and 10^{-2} {Mpc}^{-3}{Myr}^{-1} for BH-NS binaries. Mergers in elliptical galaxies are a significant fraction of our total estimate for BH-BH and BH-NS detection rates; NS-NS detection rates are dominated by the contribution from spiral galaxies. Using only models that reproduce current observations of Galactic NS-NS binaries, we find slightly higher rates for NS-NS and largely similar ranges for BH-NS and BH-BH binaries. Assuming a detection signal-to-noise ratio threshold of 8 for a single detector (as part of a network), corresponding to radii \Cv of the effective volume inside of which a single LIGO detector could observe the inspiral of two 1.4 M_\sun neutron stars of 14 Mpc and 197 Mpc, for initial and advanced LIGO, we find event rates of any merger type of 2.9* 10^{-2} -- 0.46 and 25-400 per year (at 90% confidence level), respectively. We also find that the probability P_{detect} of detecting one or more mergers with this single detector can be approximated by (i) P_{detect}\simeq 0.4+0.5\log (T/0.01{yr}), assuming \Cv=197 {Mpc} and it operates for T years, for T between 2 days and 0.1 {yr}); or by (ii) P_{detect}\simeq 0.5 + 1.5 \log \Cv/32{Mpc}, for one year of operation and for $\Cv$ between 20 and 70 Mpc. [ABRIDGED]

Where in the Virgo Cluster are Galaxies Stripped? Stellar Population Evolution of Stripped Spiral Galaxies in Virgo

The nearby Virgo Cluster provides an ideal laboratory to study galaxy-galaxy and galaxy-cluster interactions at a level of detail impossible at higher redshift. In Virgo, there exists a large population of spiral galaxies with mostly undisturbed stellar disks, but truncated gas disks. We present results of an observational study of several of these galaxies, utilizing optical and UV imaging, and optical spectroscopy. By combining optical spectroscopy and UV imaging, we are able to constrain the time since star formation ended in the outer disk and, therefore, constrain the time since the galaxies were stripped. Our results show that while most of the galaxies in our sample are consistent with being stripped near the cluster center, several show evidence for being stripped well outside the core, suggesting that the “reach” of the intracluster medium is greater than is suggested by simple ICM models.

The Structure of Rapidly Rotating Late-Type Spiral Galaxies. I. Photometry, Hi, and Optical Kinematics

We present I-band photometry, long-slit optical spectroscopy, and new aperture synthesis H I observations for eight late-type spiral galaxies with rotation velocities in the range 243 km s-1 Vrot 308 km s-1. The sample will be used to study the structure and angular momentum of disks at the high-mass end of the spiral galaxy population; here we discuss the basic properties of these fast rotators and derive hybrid optical/H I rotation curves for each. Despite the presence of H I warps and low-mass companions in many systems, their kinematics are regular and there is excellent agreement between optical and H I tracers near the optical radius ropt. At high inclinations at which projection effects are negligible, the sample galaxies exhibit flat, featureless rotation curves out to their last measured points at 1.7ropt-3.5ropt. The intermediate-inclination systems are also consistent with a constant rotation amplitude for r 0.5ropt. We therefore find no evidence for declining rotation curves at the high-mass end of the late-type spiral galaxy population. Combining our data with the compilation of spiral galaxies with reliable outer H I kinematics from the work of Casertano and van Gorkom, we find no convincing trends between logarithmic outer rotation curve slopes and rotation amplitudes or surface brightnesses for galaxies with Vrot 220 km s-1. Correlations between these slopes and morphological types or disk scale lengths are also marginal in this regime.

Optical Environments of M51 X-ray Sources

The X-ray populations of spiral galaxies consist almost entirely of accreting X-ray binaries and supernova remnants. For the most luminous sources, it is possible to use X-ray spectroscopy and variability studies to gain insights into the nature of the sources. However, without unambiguously identified optical counterparts, it is impossible to definitively classify sources as, e.g. high-mass or low-mass X-ray binaries. The nearby interacting galaxy M51 is one of the best-studied galaxies across all wavelengths. At a distance of around 8 Mpc, it is possible to resolve features on scales of a few parsecs both in the X-ray and the optical. Recently, M51 was observed with the Advanced Camera for Surveys on the Hubble Space Telescope as part of a Hubble Legacy program. M51 has also been observed 3 times with the Chandra X-ray observatory. Combining these two datasets, we present initial results on the optical environments of M51 X-ray sources as the first part of a truly multi-wavelength study of X-ray sources in nearby galaxies.

An Emission‐Line Search for Star‐forming Dwarf Galaxies toward Abell 851

We present deep images of the redshift z = 0.41 galaxy cluster Abell 851 (Cl 0939+4713) including a narrow bandwidth image of the redshifted [O II] ??3726, 3729 line emission. The [O II] doublet is the most accessible tracer of star formation out to redshifts near unity, and we use it to identify candidates for star-forming galaxies. The galaxies selected lie within a projected clustercentric distance of 2 Mpc and have line-of-sight velocities with respect to the cluster in the range of ?1460 km s-1. The sample is complete to magnitude m5129(AB) = 24.0 for galaxies with emission-line equivalent widths greater than about 11 ? in the observed frame. The sample is contaminated by foreground galaxies with a steep 4000 ? break across the filters and possibly Ly? emitters at z = 3.31, but such galaxies can be identified using color, brightness, and equivalent-width criteria. Excluding the likely interlopers, the number density of star-forming galaxies near Cl 0939+4713 is still at least 3-4 times higher than that of a similar column through the field at z = 0.4. Galaxies in the cluster sample have lower [O II] equivalent widths than similarly selected field galaxies at z ~ 0.4, however, and we suggest that while the density of galaxies is higher in the cluster the star formation activity in individual galaxies is suppressed relative to their counterparts in the field. The relatively small enhancement in the surface density of the [O II]-selected population toward the cluster core leads us to believe the [O II]-selected galaxies reside in the outer regions of the cluster. We identify a population of starburst galaxies among the [O II] emitters based on their blue g-i color. The majority of the [O II]-selected galaxies appear to be related to the normal spiral galaxy population, but the bursting population is dominated by intrinsically faint galaxies of below average size. We suggest that this population is composed primarily of dwarf galaxies and discuss their relation to the dwarf galaxies in present-day clusters.

Galaxy Morphologies in the Cluster Cl 1358+62 atz = 0.33

We describe the morphological composition of a sample of 518 galaxies in the field of Cl 1358+62 at z = 0.33, drawn from a large Hubble Space Telescope mosaic covering 53 square arcminutes. The sample is complete to I = 22, corresponding to MV = -18.5 in the rest frame. The galaxy morphologies have been independently classified by the authors of this paper and by Alan Dressler. Dressler's classifications place our work in context with the previous MORPHS study and allow us to estimate the scatter between different sets of visual classifications. We restrict most of our analysis to the brighter part of the sample, I < 21 (MV < -19.5), where the scatter between the two sets of classifications is ~1 in morphological type. The scatter doubles at I = 22, presumably owing to the lower signal-to-noise and poorer sampling of faint, small galaxy images. To I = 21 the two sets of classifiers agree on the fraction of early type galaxies (elliptical + S0): 72%. We conclude that Cl 1358+62 does not contain the large population of spiral galaxies found in other studies of clusters at z ~ 0.3 and that there is probably a significant spread in the degree of cluster evolution at intermediate redshift. The two groups of classifiers differ on the relative fraction of S0 and elliptical galaxies. We show that the distributions of ellipticities and bulge/total light cannot resolve this discrepancy. Nonetheless, we can derive significant constraints on physical models for the evolution of the galaxy population in Cl 1358+62. The higher ratio of S0 to elliptical galaxies (1.6) found by DF/MF/PvD requires that the evolution preserve the relative fraction of elliptical, S0 and spiral galaxies. Alternately, the lower ratio (1.1) found by Dressler requires that the evolution preserve the early-type to spiral ratio while increasing the S0 to elliptical ratio. In the latter case, a possible evolutionary mechanism is accretion of galaxies that predominantly evolve to S0 galaxies between z = 0.33 and the present. We use our large body of spectra to make the correspondence between spectral and morphological type. Our data follow the pattern seen in the field at low redshift: emission-line spectra are more prevalent among the later morphological types. The 11 identified k+a galaxies (absorption-line spectra with strong Balmer lines) have S0-Sb morphologies.

Environmental Extremists in the Virgo Cluster

Many types of galaxy interactions have been posited to occur in clusters, although it remains unclear which processes actually occur, and which ones might help explain the tendency for early type galaxies to inhabit high density environments, or cause the rapid evolution of cluster galaxies (e.g., Dressler et al. 1997). With these questions in mind, we have been conducting an environmental inventory of galaxies in the Virgo Cluster. Our approach is to combine surveys of spirals and S0s with detailed studies of the most interesting and peculiar galaxies. In this paper, we describe two main points. 1.) There is a population of spiral galaxies in the Virgo cluster with the small central light concentrations (bulge-to-disk ratios, or B/D's) characteristic of isolated Sb and Sc galaxies, but global star formation rates lower than those of isolated spirals of any Hubble class (Sa-Sc). These Virgo galaxies are generally classified as “early type” (e.g. Sa), and thus contribute to the morphology-density relationship. 2.) There areseveral typesof environmental interactions occurring in Virgo, including low velocity tidal interactions and mergers, high velocity tidal interactions and collisions, HI accretion, and ICM-ISM stripping. We discuss examples of some of these interactions.

The ages and metallicities of early-type galaxies in the Fornax cluster

We have measured central line strengths for a complete sample of early-type galaxies in the Fornax cluster, comprising 11 elliptical and 11 lenticular galaxies, more luminous than MB = −17. In contrast to the elliptical galaxies in the sample studied by González (and recently revisited by Trager) we find that the Fornax ellipticals follow the locus of galaxies of fixed age in Worthey's models and have metallicities varying from roughly solar to three times solar. The lenticular galaxies, however, exhibit a substantial spread to younger luminosity-weighted ages, indicating a more extended star formation history. We present measurements of the more sensitive indices: C4668 and HγA; these confirm and reinforce the conclusions that the elliptical galaxies are coeval and that only the lenticular galaxies show symptoms of late star formation. The inferred difference in the age distribution between lenticular and elliptical galaxies is a robust conclusion as the models generate consistent relative ages using different age and metallicity indicators even though the absolute ages remain uncertain. The young luminosity-weighted ages of the S0s in the Fornax cluster are consistent with the recent discovery that the fraction of S0 galaxies in intermediate-redshift clusters is a factor of 2–3 lower than found locally, and suggest that a fraction of the cluster spiral galaxy population has evolved to quiescence in the 5-Gyr interval from z = 0.5 to the present. Two of the faintest lenticular galaxies in our sample have blue continua and strong Balmer-line absorption, suggesting starbursts ≲2 Gyr ago. These may be the low-redshift analogues of the starburst or post-starburst galaxies seen in clusters at z = 0.3, similar to the Hδ-strong galaxies in the Coma cluster.

Studies of Hot B Subdwarfs. X. The Distribution and Space Density of Hot, Hydrogen-rich Subdwarfs Determined from the Palomar-Green Survey

view Abstract Citations (21) References (57) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Studies of Hot B Subdwarfs. X. The Distribution and Space Density of Hot, Hydrogen-rich Subdwarfs Determined from the Palomar-Green Survey Villeneuve, B. ; Wesemael, F. ; Fontaine, G. ; Carignan, C. ; Green, R. F. Abstract We have computed the space density, as well as the characteristic scale height of the distribution, of hot, hydrogen-rich subdwarfs in the Galaxy through the use of photoelectric Strömgren photometry of a sample of 209 of these stars culled from the Palomar-Green Survey. Homogeneous, exponential, and isothermal-sheet model distributions in the direction perpendicular to the Galactic plane are considered in turn, together with various subsamples of objects reaching down to different limiting b magnitudes. Taking into account the results of the V/Vm test on the brightest subsamples, which suggest that the PG survey might not be complete at bright magnitudes, we find that the distribution of hot, hydrogen-rich subdwarf stars can be satisfactorily reproduced with an isothermal scale height of 600±150 pc, a value characteristic of the disk population of spiral galaxies or, alternatively, with an exponential scale height of 450±150 pc. The resulting values of the space density and birthrate in both cases are (3 ± 1) × 10-7 pc-3 and ∼(1-3) × 10-15 pc-3 yr-1, a factor of ∼5-10 lower than previous estimates. Detailed comparisons with previous determinations are provided, and the implications of the large exponential scale height, and low space density and birthrate, for this particular channel of pre-white dwarf evolution are considered. Publication: The Astrophysical Journal Pub Date: June 1995 DOI: 10.1086/175824 Bibcode: 1995ApJ...446..646V Keywords: GALAXY: STRUCTURE; STARS: EARLY-TYPE; STARS: STATISTICS; STARS: SUBDWARFS full text sources ADS | data products SIMBAD (16) Related Materials (10) Part 1: 1984AJ.....89..374B Part 2: 1985ApJ...298..859W Part 3: 1985ApJ...299..496L Part 4: 1985ApJ...299..741M Part 5: 1987ApJ...318..844L Part 6: 1988ApJ...332..964B Part 7: 1989ApJ...338..417M Part 8: 1992AJ....104..203W Part 9: 1994AJ....107.1565A Part 11: 1995ApJ...450..851V

Infrared background constraints on the evolution of IRAS galaxies

Source counts and redshift surveys at 60 μm provide clear evidence of cosmological evolution of the spiral galaxy population. Preliminary results from the COBE mission and recent reanalysis of the IRAS background data provide interesting constraints on these evolutionary models. For pure density evolution at the rate needed for consistency with the source counts and redshift surveys, the 60-500 μm background limits imply that there must be a redshift cut-off (Z(max)) at Z(max) ≤ 2. For luminosity evolution, on the other hand, the predicted background is well below the currently available background limits for Z(max) ∼ 5