Apparent Axial Ratio Research Articles

Dwarf Galaxies with the Highest Concentration Are Not Thicker than Ordinary Dwarf Galaxies

The formation mechanism of high-concentration dwarf galaxies is still a mystery. We perform a comparative study of the intrinsic shape of nearby low-mass galaxies with different stellar concentration. The intrinsic shape is parameterized by the intermediate-to-major axis ratios B/A and the minor-to-major axis ratios C/A of triaxial ellipsoidal models. Our galaxies (107.5 M ⊙ < M ⋆ < 1010.0 M ⊙) are selected to have spectroscopic redshift from SDSS or GAMA and have broadband optical images from the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) wide-layer survey. The deep HSC-SSP images allow to measure the apparent axis ratios q at galactic radii beyond the central star-forming area of our galaxies. We infer the intrinsic axis ratios based on the q distributions. We find that (1) our galaxies have typical intrinsic shape similarly close to be oblate (μ B/A ∼ 0.9–1), regardless of the concentration, stellar mass, star formation activity, and local environment (being central or satellite); (2) galaxies with the highest concentration tend to have intrinsic thickness similar to or (in virtually all cases) slightly thinner (i.e., smaller mean μ C/A or equivalently lower triaxiality) than ordinary galaxies, regardless of other properties explored here. This appears to be in contrast with the expectation of the classic merger scenario for high-concentration galaxies. Given the lack of a complete understanding of dwarf–dwarf merger, we cannot draw a definite conclusion about the relevance of mergers in the formation of high-concentration dwarfs. Other mechanisms such as halo spin may also play important roles in the formation of high-concentration dwarf galaxies.

Constraining the Milky Way’s ultraviolet-to-infrared SED with Gaussian process regression

ABSTRACT Improving our knowledge of global Milky Way (MW) properties is critical for connecting the detailed measurements only possible from within our Galaxy to our understanding of the broader galaxy population. We here train Gaussian process regression (GPR) models on SDSS (Sloan Digital Sky Survey) galaxies to map from galaxy properties (stellar mass, apparent axial ratio, star formation rate, bulge-to-total ratio, disc scale length, and bar vote fraction) to ultraviolet (UV; GALEX FUV/NUV), optical (SDSS ugriz), and infrared (IR; 2MASS JHKs and WISE W1/W2/W3/W4) fluxes and uncertainties. With these models, we estimate the photometric properties of the MW, resulting in a full UV-to-IR spectral energy distribution (SED) as it would be measured externally, viewed face-on. We confirm that the MW lies in the green valley in optical diagnostic diagrams, but show for the first time that the MW is in the star-forming region in standard UV and IR diagnostics – characteristic of the population of red spiral galaxies. Although our GPR method predicts one band at a time, the resulting MW UV–IR SED is consistent with SEDs of local spirals with characteristics broadly similar to the MW, suggesting that these independent predictions can be combined reliably. Our UV–IR SED will be invaluable for reconstructing the MW’s star formation history using the same tools employed for external galaxies, allowing comparisons of results from in situ measurements to those from the methods used for extragalactic objects.

Phase equilibria in binary blends of a flexible liquid crystal polymer and rigid-rod monomers

In this study, we report on the phase equilibria in binary blends of a flexible liquid crystal polymer with non-mesogenic rigid-rod monomers. We utilized a combination of Optical Microscopic (OM) and Differential Scanning Calorimetric (DSC) methods to determine the transition temperatures, enthalpies and entropies within the total compositions of the phase diagrams. We verified the effect of molecular geometry of rigid-rod monomers on transition temperatures, enthalpies and entropies of blends and evaluated the apparent axial ratio of polymer and entropy values of nematic-isotropic phase transition. In addition, we compared our experimental nematic-isotropic phase transition data with few early lattice model theories.

Intrinsic Morphology of Ultra-diffuse Galaxies

Abstract With the published data of apparent axis ratios for 1109 ultra-diffuse galaxies (UDGs) located in 17 low-redshift (z ∼ 0.020–0.063) galaxy clusters and 84 UDGs in two intermediate-redshift (z ∼ 0.308–0.348) clusters, we take advantage of a Markov Chain Monte Carlo approach and assume a triaxial model to investigate the intrinsic morphologies of UDGs. In contrast to the conclusion of Burkert, i.e., the underlying shapes of UDGs are purely prolate (C = B &lt; A), we find that the data favor the oblate-triaxial models (i.e., thick disks with ) over the nearly prolate ones. We also find that the intrinsic morphologies of UDGs are related to their stellar masses/luminosities, environments, and redshifts. First, the more luminous UDGs have puffier morphologies compared with the less luminous counterparts; the UDG morphologic dependence on luminosity is distinct from that of the typical quiescent dwarf ellipticals (dEs) and dwarf spheroidals (dSphs); in this sense, UDGs may not be simply treated as an extension of the dE/dSph class with similar evolutionary histories; they may differ not only in size. Second, the UDGs with smaller clustercentric distances are more puffed up, compared with the counterparts with larger clustercentric distances; in combination with the UDG thickness dependence on luminosity, the puffier morphologies of UDGs with high luminosities or located in the denser environments are very likely to be attributed to tidal interactions with massive galaxies. Third, we find that the intermediate-redshift UDGs are more flattened, compared with the low-redshift counterparts, which plausibly suggests a “disky” origin for the high-redshift, newly born UDGs.

Ha Images of Ultra-Flat Edge-On Spiral Galaxies

We present the H$\alpha$ images of ultra-flat (UF) spiral galaxies seen practically edge-on. The galaxies have the angular diameter in the $B$ band $a> 1.9^{\prime}$ and the apparent axial ratio $(a/b) >10$. We found that their H$\alpha$ images look, on average, almost two times thinner than those in the red continuum. The star-formation rate in the studied objects, determined from the H$\alpha$ flux, is in good agreement with that calculated from the $FUV$ flux from the GALEX survey if we use the modified Verheijen and Sancisi formula taking into account the internal extinction in the UF galaxies. The logarithm of the specific star-formation rate in the UF galaxies shows a small scatter, $0.19$, with a smooth decrease from $-10.4$ for dwarf spirals to $-10.7$ for massive ones. The relative amount of the hydrogen mass in UF disks varies from about 50\% in dwarf disks to about 8\% in massive ones. Structural distortions are less common in the UF galaxies (about 16\%) than those in thick (less isolated) disks of edge-on spiral galaxies. On the cosmic time scale, 13.7 Gyr, large spiral disks are more efficient "engines" for gas processing into stars than dwarf spirals.

Evolution of the Three-dimensional Shape of Passively Evolving and Star-forming Galaxies at z &lt; 1

Abstract Using the HST/ACS I F814W-band data, we investigated the distribution of apparent axial ratios of ∼21,000 galaxies with M V &lt; −20 at 0.2 &lt; z &lt; 1.0 in the COSMOS field as a function of stellar mass, specific star formation rate (sSFR), and redshift. We statistically estimated intrinsic 3D shapes of these galaxies by fitting the axial-ratio distribution with triaxial ellipsoid models characterized by face-on (middle-to-long) and edge-on (short-to-long) axial ratios B/A and C/A. We found that the transition from thin disk to thick spheroid occurs at ΔMS ∼ −1 dex, i.e., 10 times lower sSFR than that of the main sequence for galaxies with M star = 1010–1011 M ⊙ at 0.2 &lt; z &lt; 1.0. Furthermore, the intrinsic thickness (C/A) of passively evolving galaxies with M star = 1010–1011 M ⊙ significantly decreases with time from C/A ∼ 0.40–0.50 at z ∼ 0.8 to C/A ∼ 0.33–0.37 at z ∼ 0.4, while those galaxies with M star &gt; 1011 M ⊙ have C/A ∼ 0.5 irrespective of redshift. On the other hand, star-forming galaxies on the main sequence with 109.5–1011 M ⊙ show no significant evolution in their shape at 0.2 &lt; z &lt; 1.0, but their thickness depends on stellar mass; more massive star-forming galaxies tend to have lower C/A (thinner shape) than low-mass ones. These results suggest that some fraction of star-forming galaxies with a thin disk, which started to appear around z ∼ 1, quench their star formation without violent morphological change, and these newly added quiescent galaxies with a relatively thin shape cause the significant evolution in the axial-ratio distribution of passively evolving galaxies with M star &lt; 1011 M ⊙ at z &lt; 1.

An ALMA survey of the SCUBA-2 Cosmology Legacy Survey UKIDSS/UDS field: high-resolution dust continuum morphologies and the link between sub-millimetre galaxies and spheroid formation

ABSTRACT We present an analysis of the morphology and profiles of the dust continuum emission in 153 bright sub-millimetre galaxies (SMGs) detected with ALMA at signal-to-noise ratios of &gt;8 in high-resolution 0.18 arcsec (∼1 kpc) 870 $\mu$m maps. We measure sizes, shapes, and light profiles for the rest-frame far-infrared emission from these luminous star-forming systems and derive a median effective radius (Re) of 0.10 ± 0.04 arcsec for our sample with a median flux of S870 = 5.6 ± 0.2 mJy. We find that the apparent axial ratio (b/a) distribution of the SMGs peaks at b/a ∼ 0.63 ± 0.02 and is best described by triaxial morphologies, while their emission profiles are best fitted by a Sérsic model with n ≃ 1.0 ± 0.1, similar to exponential discs. This combination of triaxiality and n ∼ 1 Sérsic index are characteristic of bars and we suggest that the bulk of the 870 $\mu$m dust continuum emission in the central ∼2 kpc of these galaxies arises from bar-like structures. As such we caution against using the orientation of shape of the bright dust continuum emission at $\eqsim$ resolution to assess either the orientation of any disc on the sky or tits inclination. By stacking our 870 $\mu$m maps we recover faint extended dust continuum emission on ∼4 kpc scales which contributes 13 ± 1 per cent of the total 870 $\mu$m emission. The scale of this extended emission is similar to that seen for the molecular gas and rest-frame optical light in these systems, suggesting that it represents an extended dust and gas disc at radii larger than the more active bar component. Including this component in our estimated size of the sources we derive a typical effective radius of ≃0.15 ± 0.05 arcsec or 1.2 ± 0.4 kpc. Our results suggest that kpc-scale bars are ubiquitous features of high star-formation rate systems at $z$ ≫ 1, while these systems also contain fainter and more extended gas and stellar envelopes. We suggest that these features, seen some 10–12 Gyr ago, represent the formation phase of the earliest galactic-scale components: stellar bulges.

A reference sample of face-on bulgeless galaxies

Abstract We present a list of 220 face-on, almost bulgeless galaxies assumed to be counterparts to the objects from the Reference Flat Galaxy Catalogue (RFGC). We selected the Sc-, Scd-, and Sd-type galaxies according to their apparent axial ratio log(r25) &lt; 0.05 and major standard angular diameter log(d25) &gt; 0.90 as defined in HyperLEDA. The sample objects are restricted by the radial velocity $V_{\mathrm{ LG}} \lt 10\, 000$ km s−1 and a declination of above –30 deg. The morphological composition of our sample is quite similar to that of RFGC. We notice the following common properties of face-on bulgeless galaxies. About half of them have bar-like structures occurring in the whole range of the absolute magnitudes of galaxies: from −17 to −22 mag. An essential part of our sample (27–50 per cent) exhibit distorted spiral patterns. The galaxies do not show significant asymmetry in numbers of the ‘S’- and ‘Z’-like spin orientation. The mean (pseudo-)bulge-to-total mass ratio for the sample is estimated as 0.11. Due to a negligible internal extinction, low-light background, and small projection effect, the face-on Sc–Sd discs are suitable objects to recognize their central nuclei as moderate-mass BH candidates. About 40–60 per cent of the galaxies have distinct unresolved nuclei, and their presence steeply depends on the luminosity of the host galaxy.

High-redshift Massive Quiescent Galaxies Are as Flat as Star-forming Galaxies: The Flattening of Galaxies and the Correlation with Structural Properties in CANDELS/3D-HST

Abstract We investigate the median flattening of galaxies at 0.2 &lt; z &lt; 4.0 in all five CANDELS/3D-HST fields via the apparent axis ratio, q. We separate the sample into bins of the redshift, stellar mass, Sérsic index, size, and UVJ-determined star-forming state to discover the most important drivers of the median q (q med). Quiescent galaxies at z &lt; 1 and M * &gt; 1011 M ⊙ are rounder than those at lower masses, consistent with the hypothesis that they have grown significantly through dry merging. The massive quiescent galaxies at higher redshifts become flatter and are as flat as star-forming massive galaxies at 2.5 &lt; z &lt; 3.5, consistent with formation through direct transformations or wet mergers. We find that in quiescent galaxies, correlations with q med and M *, and z and r e are driven by the evolution in the Sérsic index (n), consistent with the growing accumulation of minor mergers at lower redshifts. Interestingly, n does not drive these trends fully in star-forming galaxies. Instead, the strongest predictor of q in star-forming galaxies is the effective radius, where larger galaxies are flatter. Our findings suggest that q med is the tracing bulge-to-total ratio, which would explain why smaller/more massive star-forming galaxies are rounder than their extended/less massive analogs, although it is unclear why the Sérsic index correlates more weakly with flattening for star-forming galaxies than for quiescent galaxies.

Ultra-flat galaxies selected from RFGC catalog. III. Star formation rate

We examine the star formation properties of galaxies with very thin disks selected from the Revised Flat Galaxy Catalog (RFGC). The sample contains 333 ultra-flat galaxies (UFG) at high Galactic latitudes, $|b|>10^{\circ}$, with a blue major angular diameter of $a\geq 1.2^{\prime}$, blue and red apparent axial ratios of $(a/b)_b > 10$, $(a/b)_r > 8.5$ and radial velocities within 10000~km s$^{-1}$. As a control sample for them we use a population of 722 more thick RFGC galaxies with $(a/b)_b > 7$, situated in the same volume. The UFG distribution over the sky indicates them as a population of quite isolated galaxies. We found that the specific star formation rate, sSFR FUV, determined via the FUV GALEX flux, increases steadily from the early type to late type disks for both the UFG and RFGC-UFG samples, showing no significant mutual difference within each morphological type T. The population of UFG disks has the average H,I-mass-to-stellar-mass ratio by $(0.25\pm0.03)$ dex higher than that of RFGC--UFG galaxies. Being compared with arbitrary orientated disks of the same type, the ultra-flat edge-on galaxies reveal that their total H,I mass is hidden by self-absorption on the average by approximately 0.20 dex. We demonstrate that using the robust stellar mass estimate via $\langle B-K \rangle$-color and galaxy type T for the thin disks, together with a nowaday accounting for internal extinction, yields their sSFR quantities definitely lying below the limit of $-9.4$ dex,(yr$^{-1}$). The collected observational data on UFG disks imply that their average star formation rate in the past has been approximately three times the current SFR. The UFG galaxies have also sufficient amount of gas to support their observed SFR over the following nearly 9 Gyrs.

Ultra-flat galaxies selected from RFGC catalog. II. Orbital estimates of halo masses

We used the Revised Flat Galaxy Catalog (RFGC) to select 817 ultra-flat (UF) edge-on disk galaxies with blue and red apparent axial ratios of $(a/b)_B > 10.0$ and $(a/b)_R > 8.5$. The sample covering the whole sky, except the Milky Way zone, contains 490 UF galaxies with measured radial velocities. Our inspection of the neighboring galaxies around them revealed only 30 companions with radial velocity difference of $\mid\Delta V\mid<500$ km s$^{-1}$ inside the projected separation of $R_p < 250$ kpc. Wherein, the wider area around the UF galaxy within $R_p < 750$ kpc contains no other neighbors brighter than the UF galaxy itself in the same velocity span. The resulting sample galaxies mostly belong to the morphological types Sc, Scd, Sd. They have a moderate rotation velocity curve amplitude of about $120$ km s$^{-1}$ and a moderate K-band luminosity of about $10^{10}L_{\odot}$. The median difference of radial velocities of their companions is $87$ km s$^{-1}$, yielding the median orbital mass estimate of about $5\times10^{11}M_{\odot}$. Excluding six probable non-isolated pairs, we obtained a typical halo-mass-to-stellar-mass of UF galaxies of about $30$, what is almost the same one as in the principal spiral galaxies, like M 31 and M 81 in the nearest groups. We also note that ultra-flat galaxies look two times less "dusty" than other spirals of the same luminosity.

THE NEXT GENERATION VIRGO CLUSTER SURVEY. VII. THE INTRINSIC SHAPES OF LOW-LUMINOSITY GALAXIES IN THE CORE OF THE VIRGO CLUSTER, AND A COMPARISON WITH THE LOCAL GROUP

ABSTRACT We investigate the intrinsic shapes of low-luminosity galaxies in the central 300 kpc of the Virgo Cluster using deep imaging obtained as part of the Next Generation Virgo Cluster Survey (NGVS). We build a sample of nearly 300 red-sequence cluster members in the yet-unexplored −14 &lt; M g &lt; −8 mag range, and we measure their apparent axis ratios, q, through Sérsic fits to their two-dimensional light distribution, which is well described by a constant ellipticity parameter. The resulting distribution of apparent axis ratios is then fit by families of triaxial models with normally distributed intrinsic ellipticities, E = 1 − C/A, and triaxialities, T = (A 2 − B 2)/(A 2 − C 2). We develop a Bayesian framework to explore the posterior distribution of the model parameters, which allows us to work directly on discrete data, and to account for individual, surface-brightness-dependent axis ratio uncertainties. For this population we infer a mean intrinsic ellipticity E &macr; ?> = 0.43 - 0.02 &plus; 0.02 ?> and a mean triaxiality T &macr; ?> = 0.16 - 0.06 &plus; 0.07 ?> . This implies that faint Virgo galaxies are best described as a family of thick, nearly oblate spheroids with mean intrinsic axis ratios 1:0.94:0.57. The core of Virgo lacks highly elongated low-luminosity galaxies, with 95% of the population having q &gt; 0.45. We additionally attempt a study of the intrinsic shapes of Local Group (LG) satellites of similar luminosities. For the LG population we infer a slightly larger mean intrinsic ellipticity E &macr; ?> = 0.51 - 0.06 &plus; 0.07 ?> , and the paucity of objects with round apparent shapes translates into more triaxial mean shapes, 1:0.76:0.49. Numerical studies that follow the tidal evolution of satellites within LG-sized halos are in good agreement with the inferred shape distributions, but the mismatch for faint galaxies in Virgo highlights the need for more adequate simulations of this population in the cluster environment. We finally compare the intrinsic shapes of NGVS low-mass galaxies with samples of more massive quiescent systems, and with field, star-forming galaxies of similar luminosities. We find that the intrinsic flattening in this low-luminosity regime is almost independent of the environment in which the galaxy resides, but there is a hint that objects may be slightly rounder in denser environments. The comparable flattening distributions of low-luminosity galaxies that have experienced very different degrees of environmental effects suggest that internal processes are the main drivers of galaxy structure at low masses, with external mechanisms playing a secondary role.

Ultra-flat galaxies selected from RFGC catalog. I. The sample properties

We used the Revised Flat Galaxy Catalog (RFGC) to create a sample of ultra-flat galaxies (UFG) covering the whole northern and southern sky apart from the Milky Way zone. It contains 817 spiral galaxies seen edge-on, selected into the UFG sample according to their apparent axial ratios $(a/b)_B\geq10.0$ and $(a/b)_R\geq8.53$ in the blue and red bands, respectively. Within this basic sample we fixed an exemplary sample of 441 UFG galaxies having the radial velocities of $V_{LG} < 10000$ km s$^{-1}$, Galactic latitude of $\mid b\mid>10^{\circ}$ and the blue angular diameter of $a_B > 1.0^{\prime}$. According to the Schmidt test the exemplary sample of 441 galaxies is characterized by about (80-90)% completeness, what is quite enough to study different properties of the ultra-flat galaxies. We found that more than 3/4 of UFGs have the morphological types within the narrow range of $T= 7\pm1$, i.e. the thinnest stellar disks occur among the Scd, Sd, and Sdm types. The average surface brightness of UFG galaxies tends to diminish towards the flattest bulge-less galaxies. Regularly shaped disks without signs of asymmetry make up about 2/3 both among all the RFGC galaxies, and the UFG sample objects. About 60% of ultra-flat galaxies can be referred to dynamically isolated objects, while 30% of them probably belong to the scattered associations (filaments, walls), and only about 10% of them are dynamically dominating galaxies with respect to their neighbours.

WHEN DID ROUND DISK GALAXIES FORM?

When and how galaxy morphology such as disk and bulge seen in the present-day universe emerged is still not clear. In the universe at $z\gtrsim 2$, galaxies with various morphology are seen, and star-forming galaxies at $z\sim2$ show an intrinsic shape of bar-like structure. Then, when did round disk structure form? Here we take a simple and straightforward approach to see the epoch when a round disk galaxy population emerged by constraining the intrinsic shape statistically based on apparent axial ratio distribution of galaxies. We derived the distributions of the apparent axial ratios in the rest-frame optical light ($\sim 5000$ \AA) of star-forming main sequence galaxies at $2.5>z>1.4$, $1.4>z>0.85$, and $0.85>z>0.5$, and found that the apparent axial ratios of them show peaky distributions at $z\gtrsim0.85$, while a rather flat distribution at the lower redshift. By using a tri-axial model ($A>B>C$) for the intrinsic shape, we found the best-fit models give the peaks of the $B/A$ distribution of $0.81\pm0.04$, $0.84\pm0.04$, and $0.92\pm0.05$ at $2.5>z>1.4$, $1.4>z>0.85$, and $0.85>z>0.5$, respectively. The last value is close to the local value of 0.95. Thickness ($C/A$) is $\sim0.25$ at all the redshifts and is close to the local value (0.21). The results indicate the shape of the star-forming galaxies in the main sequence changes gradually, and the round disk is established at around $z\sim0.9$. Establishment of the round disk may be due to a cease of violent interaction of galaxies or a growth of a bulge and/or a super-massive black hole resides at the center of a galaxy which dissolves the bar structure.

INTRINSIC SHAPE OF STAR-FORMING BzK GALAXIES. II. REST-FRAME ULTRAVIOLET AND OPTICAL STRUCTURES IN GOODS-SOUTH AND SXDS

(Abridge) We study statistical intrinsic shape of star-forming BzK galaxies (sBzK galaxies) at z~2 in both rest-frame UV and rest-frame optical wavelengths. The sBzK galaxies are selected down to K(AB)=24.0 mag in the GOODS-South and SXDS fields, where high-resolution images from Hubble Space Telescope are publicly available. 57% (583) of all 1028 galaxies in GOODS-S show a single component in the ACS/F850LP image. As WFC3/F160W images cover only some part of GOODS-S and SXDS, 724/1028 and 2500/29835 sBzK galaxies in the GOODS-S and SXDS have the WFC3 coverage. 86% (626) and 82% (2044) of the sBzK galaxies in WFC3/F160W images appear as a single component in the GOODS-S and SXDS, respectively. Larger fraction of single-component objects in F850LP images represents multiple star-forming regions in galaxies, while they are not so obvious in the F160W image which appears smoother. Most of the single-component sBzK galaxies show S\'ersic indices of n=0.5-2.5, in agreement with those of local disk galaxies. Their effective radii are 1.0-3.0 kpc and 1.5-4.0 kpc in F850LP and F160W images, respectively, regardless of the observed fields. Stellar surface mass density of the sBzK galaxies is also comparable to that of the local disk galaxies. However, the intrinsic shape of sBzK galaxies is not a round disk as seen in the local disk galaxies. By comparing apparent axial ratio (b/a) distributions of the sBzK galaxies with those by assuming tri-axial model with axes A>B>C, we found their intrinsic face-on B/A ratios peak at B/A=0.70 and B/A=0.77-0.79 in the rest-frame UV and optical, respectively and are statistically more bar-like than that of the local disk galaxies. The intrinsic edge-on C/A ratios in both rest-frame UV and optical wavelengths peak at 0.26, which is slightly larger than that of the local disk galaxies.

INTRINSIC SHAPE OF STAR-FORMING BzK GALAXIES ATz∼ 2 IN GOODS-N

We study structure of star-forming galaxies at z~2 in GOODS-N field selected as sBzK galaxies down to K_{AB} <24.0 mag. Among 1029 sBzK galaxies, 551 galaxies (54%) show a single component in ACS/F850LP image obtained with the Hubble Space Telescope; the rest show multiple components. We fit the single-component sBzK galaxies with the single S\'ersic profile using the ACS/F850LP image and find that a majority of them (64%) show S\'ersic index of n=0.5-2.5, indicating that they have a disk-like structure. The resulting effective radii typically range from 1.0 to 3.0 kpc in the rest-frame UV wavelength. After correcting the effective radii to those in the rest-frame optical wavelength, we find that the single-component sBzK galaxies locate in the region where the local and z~1 disk galaxies distribute in the stellar mass-size diagram, suggesting comparable surface stellar mass density between the sBzK and z~0-1 disk galaxies. All these properties suggest that the single-component sBzK galaxies are progenitors of the present-day disk galaxies. However, by studying their intrinsic shape through comparison between the observed distribution of apparent axial ratios and the distribution for triaxial models with axes (A>B>C), we find that the mean B/A ratio is 0.61^{+0.05}_{-0.08} and disk thickness C/A is 0.28^{+0.03}_{-0.04}. This indicates that the single-component sBzK galaxies at z~2 have a bar-like or oval shape rather than a round disk shape. The shape seems to resemble to a bar/oval structure that form through bar instability; if it is the case, the intrinsic shape may give us a clue to understand dynamical evolution of baryonic matter in a dark matter halo.

Thin discs, thick dwarfs and the effects of stellar feedback

Abstract We investigate the role of stellar mass in shaping the intrinsic thickness of galaxy discs by determining the probability distribution of apparent axial ratios (b/a) for two different samples that probe the faint end of the galaxy luminosity function. We find that the b/a distribution has a characteristic ‘U-shape’ and identify a limiting mass M*≈ 2 × 109M⊙ below which low-mass galaxies start to be systematically thicker. This tendency holds for very faint (MB∼−8) dwarfs in the local volume, which are essentially spheroidal systems. We argue that galaxy shape is the result of the complex interplay between mass, specific angular momentum and stellar feedback effects. Thus, the increasing importance of turbulent motions in lower mass galaxies leads to the formation of thicker systems, a result supported by the latest hydrodynamical simulations of dwarf galaxy formation and other theoretical expectations. We discuss several implications of this finding, including the formation of bars in faint galaxies, the deprojection of Hi line profiles and simulations of environmental effects on the dwarf galaxy population.

Thick gas discs in faint dwarf galaxies

Abstract We determine the intrinsic axial ratio distribution of the gas discs of extremely faint MB &amp;lt; −14.5 dwarf irregular galaxies. We start with the measured (beam corrected) distribution of apparent axial ratios in the Hi 21-cm images of dwarf irregular galaxies observed as part of the Faint Irregular Galaxy GMRT Survey (FIGGS). Assuming that the discs can be approximated as oblate spheroids, the intrinsic axial ratio distribution can be obtained from the observed apparent axial ratio distribution. We use a variety of methods to do this, and our final results are based on using Lucy's deconvolution algorithm. This method is constrained to produce physically plausible distributions, and also has the added advantage of allowing for observational errors to be accounted for. While one might a priori expect that gas discs would be thin (because collisions between gas clouds would cause them to quickly settle down to a thin disc), we find that the Hi discs of faint dwarf irregulars are quite thick, with mean axial ratio 〈q〉∼ 0.6. While this is substantially larger than the typical value of ∼0.2 for the stellar discs of large spiral galaxies, it is consistent with the much larger ratio of velocity dispersion to rotational velocity (σ/vc) in dwarf galaxy Hi discs as compared to that in spiral galaxies. Our findings have implications for studies of the mass distribution and the Tully–Fisher relation for faint dwarf irregular galaxies, where it is often assumed that the gas is in a thin disc.

The shapes of BCGs and normal ellipticals in nearby clusters

We compare the apparent axial ratio distributions of Brightest Cluster Galaxies (BCGs) and normal ellipticals (Es) in our sample of 75 galaxy clusters from the WINGS survey. Most BCGs in our clusters (69%) are classified as cD galaxies. The sample of cDs has been completed by 14 additional cDs (non-BCGs) we found in our clusters. We find that: (i) Es have triaxial shape, the triaxiality sharing almost evenly the intrinsic axial ratios parameter space, with a weak preference for prolateness; (ii) the BCGs have triaxial shape as well. However, their tendence towards prolateness is much stronger than in the case of Es. Such a strong prolateness appears entirely due to the sizeable (dominant) component of cDs inside the WINGS sample of BCGs. In fact, while the 'normal'(non-cD) BCGs do not differ from Es, as far as the shape distribution is concerned, the axial ratio distribution of BCG_cD galaxies is found to support quite prolate shapes; (iii) our result turns out to be strongly at variance with the only similar, previous analysis by Ryden et al.(1993)(RLP93), where BCGs and Es were found to share the same axial ratio distribution; (iv) our data suggest that the above discrepancy is mainly caused by the different criteria that RLP93 and ourselves use to select the cluster samples, coupled with a preference of cDs to reside in powerful X-ray emitting clusters; (v) the GIF2 N-body results suggest that the prolateness of the BCGs (in particular the cDs) could reflect the shape of the associated dark matter halos.

A catalog of Kazarian galaxies

The entire Kazarian galaxies (KG) catalog is presented, which combines extensive new measurements of their optical parameters with a literature and database search. The measurements were made using images extracted from the STScI Digitized Sky Survey (DSS) of Jpg(blue), Fpg(red), and Ipg(NIR) band photographic sky survey plates obtained by the Palomar and UK Schmidt telescopes. We provide accurate coordinates, morphological types, spectral and activity classes, blue apparent diameters, axial ratios, position angles, red, blue, and NIR apparent magnitudes, as well as counts of neighboring objects in a circle of radius 50 kpc from centers of KG. Special attention was paid to the individual descriptions of the galaxies in the original Kazarian lists, which clarified many cases of misidentifications of the objects, particularly among interacting systems. The total number of individual Kazarian objects in the database is now 706. We also include the redshifts, which are now available for 404 galaxies and the 2MASS infrared magnitudes for 598 KG. The database also includes extensive notes, which summarize information about the membership of Kazarian galaxies in different systems of galaxies and about revised activity classes and redshifts. An atlas of several interesting subclasses of Kazarian galaxies is also presented.