The Extinction Distribution in the Galaxy UGC 5041

We probe the dust extinction through the foreground disk of the overlapping galaxy pair UGC 5041 by analyzing B,I, and H band images. The inclined foreground disk of this infrared-selected pair is almost opaque in B at a projected distance of ~8kpc. From the images, we estimate directly the area-weighted distribution of differential near-IR extinction: it is nearly Gaussian with =0.6 and sigma=0.27. For a homogenous dust distribution and a Milky Way extinction curve, this corresponds to a face-on distribution p(tau) with a mean of =0.34 and sigma_V=0.15. For a clumpy dust model the optical depth estimate increases to =0.41 and sigma_V=0.19. Even though the galaxy pair is subject to different selection biases and our analysis is subject to different systematics, the result is consistent with existing case studies, indicating that ~0.3 is generic for late-type spirals near their half-light radii. We outline how to estimate from p(tau) by how much background quasars are underreresented, where projected within ~10kpc of nearby spirals, such as damped Ly-alpha absorbers or gravitational lenses; from our data we derive a factor of two deficit for flux-limited, optical surveys.Comment: 18 pages, 3 figures; To appear in the Astronomical Journa

The origin of galaxy scaling laws in LCDM

It has long been recognized that tight relations link the mass, size, and characteristic velocity of galaxies. These scaling laws reflect the way in which baryons populate, cool, and settle at the center of their host dark matter halos; the angular momentum they retain in the assembly process; as well as the radial distribution and mass scalings of the dark matter halos. There has been steady progress in our understanding of these processes in recent years, mainly as sophisticated N-body and hydrodynamical simulation techniques have enabled the numerical realization of galaxy models of ever increasing complexity, realism, and appeal. These simulations have now clarified the origin of these galaxy scaling laws in a universe dominated by cold dark matter: these relations arise from the tight (but highly non-linear) relations between (i) galaxy mass and halo mass, (ii) galaxy size and halo characteristic radius; and (iii) from the self-similar mass nature of cold dark matter halo mass profiles. The excellent agreement between simulated and observed galaxy scaling laws is a resounding success for the LCDM cosmogony on the highly non-linear scales of individual galaxies.Comment: Contribution to the Proceedings of the Simons Conference "Illuminating Dark Matter", held in Kruen, Germany, in May 2018, eds. R. Essig, K. Zurek, J. Fen

Fitting functions for a disk-galaxy model with different LCDM-halo profiles

We present an adaptation of the standard scenario of disk-galaxy formation to the concordant LCDM cosmology aimed to derive analytical expressions for the scale length and rotation speed of present-day disks that form within four different, cosmologically motivated protogalactic dark matter halo-density profiles. We invoke a standard galaxy-formation model that includes virial equilibrium of spherical dark halos, specific angular momentum conservation during gas cooling, and adiabatic halo response to the gas inflow. The mean mass-fraction and mass-to-light ratio of the central stellar disk are treated as free parameters whose values are tuned to match the zero points of the observed size-luminosity and circular speed-luminosity relations of galaxies. We supply analytical formulas for the characteristic size and rotation speed of disks built inside Einasto r^{1/6}, Hernquist, Burkert, and Navarro-Frenk-White dark matter halos. These expressions match simultaneously the observed zero points and slopes of the different correlations that can be built in the RVL space of disk galaxies from plausible values of the galaxy- and star-formation efficiencies

Observational biases in Lagrangian reconstructions of cosmic velocity fields

Lagrangian reconstruction of large-scale peculiar velocity fields can be strongly affected by observational biases. We develop a thorough analysis of these systematic effects by relying on specially selected mock catalogues. For the purpose of this paper, we use the MAK reconstruction method, although any other Lagrangian reconstruction method should be sensitive to the same problems. We extensively study the uncertainty in the mass-to-light assignment due to luminosity incompleteness, and the poorly-determined relation between mass and luminosity. The impact of redshift distortion corrections is analyzed in the context of MAK and we check the importance of edge and finite-volume effects on the reconstructed velocities. Using three mock catalogues with different average densities, we also study the effect of cosmic variance. In particular, one of them presents the same global features as found in observational catalogues that extend to 80 Mpc/h scales. We give recipes, checked using the aforementioned mock catalogues, to handle these particular observational effects, after having introduced them into the mock catalogues so as to quantitatively mimic the most densely sampled currently available galaxy catalogue of the nearby universe. Once biases have been taken care of, the typical resulting error in reconstructed velocities is typically about a quarter of the overall velocity dispersion, and without significant bias. We finally model our reconstruction errors to propose an improved Bayesian approach to measure Omega_m in an unbiased way by comparing the reconstructed velocities to the measured ones in distance space, even though they may be plagued by large errors. We show that, in the context of observational data, a nearly unbiased estimator of Omega_m may be built using MAK reconstruction.Comment: 29 pages, 21 figures, 6 tables, Accepted by MNRAS on 2007 October 2. Received 2007 September 30; in original form 2007 July 2

The Tully-Fisher Relation and Its Residuals for a Broadly Selected Sample of Galaxies

We measure the relation between galaxy luminosity and disk circular velocity (the Tully-Fisher [TF] relation), in the g, r, i, and z-bands, for a broadly selected sample of galaxies from the Sloan Digital Sky Survey, with the goal of providing well defined observational constraints for theoretical models of galaxy formation. The input sample of 234 galaxies has a roughly flat distribution of absolute magnitudes in the range -18.5 > Mr > -22, and our only morphological selection is an axis-ratio cut b/a < 0.6 to allow accurate inclination corrections. Long-slit spectroscopy yields usable H-alpha rotation curves for 162 galaxies. Observational errors, including distance errors due to peculiar velocities, are small compared to the intrinsic scatter of the TF relation. The slope of the forward TF relation steepens from -5.5 +/- 0.2 mag/log(km/s) in the g-band to -6.6 +/- 0.2 mag/log(km/s) in the z-band. The intrinsic scatter is approximately 0.4 mag in all bands. The scatter is not dominated by rare outliers or by any particular class of galaxies, though it drops slightly, to 0.36 mag, if we restrict the sample to nearly bulgeless systems. Correlations of TF residuals with other galaxy properties are weak: bluer galaxies are significantly brighter than average in the g-band but only marginally brighter in the i-band; more concentrated galaxies are slightly fainter than average; and the TF residual is virtually independent of half-light radius, contrary to the trend expected for gravitationally dominant disks. The observed residual correlations do not account for most of the intrinsic scatter, implying that this scatter is instead driven largely by variations in the ratio of dark to luminous matter within the disk galaxy population.Comment: 23 figures, accepted by AJ, includes cosmological corrections to the dat

MASSIV: Mass Assembly Survey with SINFONI in VVDS. IV. Fundamental relations of star-forming galaxies at 1<z< 1.6

How mass assembly occurs in galaxies and which process(es) contribute to this activity are among the most highly debated questions in galaxy formation theories. This has motivated our survey MASSIV of 0.9<z<1.9 star-forming galaxies selected from the purely flux-limited VVDS redshift survey. For the first time, we derive the relations between galaxy size, mass, and internal velocity, and the baryonic Tully-Fisher relation, from a statistically representative sample of star-forming galaxies. We find a dynamical mass that agrees with those of rotating galaxies containing a gas fraction of ~20%, perfectly consistent with the content derived using the Kennicutt-Schmidt formulation and the expected evolution. Non-rotating galaxies have more compact sizes for their stellar component, and are less massive than rotators, but do not have statistically different sizes for their gas-component. We measure a marginal evolution in the size-stellar mass and size-velocity relations in which discs become evenly smaller with cosmic time at fixed stellar mass or velocity, and are less massive at a given velocity than in the local Universe. The scatter in the Tully-Fisher relation is smaller when we introduce the S05 index, which we interpret as evidence of an increase in the contribution to galactic kinematics of turbulent motions with cosmic time. We report a persistently large scatter for rotators in our relations, that we suggest is intrinsic, and possibly caused by complex physical mechanism(s) at work in our stellar mass/luminosity regime and redshift range. Our results consistently point towards a mild, net evolution of these relations, comparable to those predicted by cosmological simulations of disc formation for at least 8Gyr and a dark halo strongly coupled with galactic spectrophotometric properties

Do the Infrared Emission Features Need Ultraviolet Excitation? The PAH Model in UV-Poor Reflection Nebulae

One of the major challenges to identification of the 3.3, 6.2, 7.7, 8.6, and 11.3um interstellar IR emission bands with polycyclic aromatic hydrocarbon (PAH) molecules has been the recent detection of these bands in regions with little UV illumination, since small, neutral PAH molecules have little or no absorption at visible wavelengths and therefore require UV photons for excitation. We show here that our "astronomical" PAH model, incorporating the experimental result that the visual absorption edge shifts to longer wavelength upon ionization and/or as the PAH size increases, can closely reproduce the observed infrared emission bands of vdB 133, a UV-poor reflection nebula. It is also shown that single-photon heating of ``astronomical'' PAHs in reflection nebulae near stars as cool as T_eff=3000K can result in observable emission at 6.2, 7.7, 8.6, and 11.3um. Illustrative mid-IR emission spectra are also calculated for reflection nebulae illuminated by cool stars with T_eff=3500, 4500, 5000K. These will allow comparison with future Space Infrared Telescope Facility (SIRTF) observations of vdB 135 (T_eff=3600K), vdB 47 (T_eff=4500K), and vdB 101 (T_eff=5000K). It is also shown that the dependence of the 12um IRAS emission relative to the total far-IR emission on the effective temperature of the exciting star is consistent with the PAH model expectation for 3000K < T_eff < 30000K.Comment: 12 pages. Submitted to The Astrophysical Journal Letter

HI Selected Galaxies in the Sloan Digital Sky Survey I: Optical Data

We present the optical data for 195 HI-selected galaxies that fall within both the Sloan Digital Sky Survey (SDSS) and the Parkes Equatorial Survey (ES). The photometric quantities have been independently recomputed for our sample using a new photometric pipeline optimized for large galaxies, thus correcting for SDSS's limited reliability for automatic photometry of angularly large or low surface brightness (LSB) galaxies. We outline the magnitude of the uncertainty in the SDSS catalog-level photometry and derive a quantitative method for correcting the over-sky subtraction in the SDSS photometric pipeline. The main thrust of this paper is to present the ES/SDSS sample and discuss the methods behind the improved photometry, which will be used in future scientific analysis. We present the overall optical properties of the sample and briefly compare to a volume-limited, optically-selected sample. Compared to the optically-selected SDSS sample (in the similar volume), HI-selected galaxies are bluer and more luminous (fewer dwarf ellipticals and more star formation). However, compared to typical SDSS galaxy studies, which have their own selection effects, our sample is bluer, fainter and less massive.Comment: 14 pages, 8 Figures, accepted for publication in AJ. Complete tables will be available in the AJ electronic version and on the Vizier sit

Off-nuclear star formation and obscured activity in the luminous infrared galaxy NGC 2623

New optical Hubble Space Telescope (HST), Spitzer Space Telescope, and XMM observations of the luminous infrared galaxy (LIRG) NGC 2623 are presented. This galaxy was observed as part of the Great Observatories All-sky LIRG Survey (GOALS). The prominent 3.2 kpc southern extension to the nucleus has been resolved by HST observations into ~100 star clusters, making it one of the richest off-nuclear concentrations of bright clusters observed in GOALS. The clusters have M_(F555W) ~-6.6 to -12.6 mag, which is within the magnitude range of Antennae galaxy clusters and in excess of 30 Doradus clusters at the high end. Their optical colors are primarily consistent with ages of ~1–100 Myr. Archival GALEX data show the off-nuclear region to be extremely bright in the far-ultraviolet, being equivalent in luminosity to the resolved nuclear region at 0.15 µm, but becoming less energetically significant at increasing wavelengths. In addition, [Ne v] 14.3 µm emission is detected with Spitzer IRS, confirming the inference from the X-ray and radio data that an active galactic nucleus (AGN) is present. Thus, the off-nuclear optical clusters are associated with a secondary burst of activity corresponding to a star formation rate ~0.1–0.2 M⊙ yr^(-1); the bulk of infrared (and thus bolometric) luminosity is generated via star formation and an AGN embedded behind dust within the inner kiloparsec of the system. If the infrared luminosity is primarily reprocessed starlight, the off-nuclear starburst accounts for <1% of the present star formation in NGC 2623