Internal Extinction Research Articles

Internal and Collective Properties of Galaxies in the Sloan Digital Sky Survey

We examine volume-limited samples from the SDSS galaxies to look for relations among internal and collective physical parameters of galaxies as faint as M_r=- 17.5, which include morphology, luminosity, color, color gradient, concentration, size, velocity dispersion, equivalent width (EW) of H_alpha line,axis ratio, the luminosity and velocity dispersion functions. At fixed morphology and luminosity, we find that bright (M_r<-20) early-types show very small dispersions in color, color gradient, concentration, size, and velocity dispersion. These dispersions increase at fainter magnitudes, where the fraction of blue early-types increases. Late-types show wider dispersions in all physical parameters compared to early types at the same luminosity. Concentration indices of early-types are well-correlated with velocity dispersion, but are insensitive to luminosity and color for bright galaxies. The slope of the Faber-Jackson relation continuously changes from 4.6 +- 0.4 to 2.7+- 0.2 when luminosity changes from M_r = -22 to -20. The size of early- types is well-correlated with stellar velocity dispersion (for >100 km/s). We find that passive spirals are well-separated from star-forming late-types at EW (H_alpha) of about 4. An interesting finding is that many physical parameters of galaxies manifest different behaviors across the absolute magnitude of about M_* +- 1. The morphology fraction as a function of luminosity depends less sensitively on large scale structure than the luminosity function (LF) does, and thus seems to be more universal. The effects of internal extinction in late-types on the completeness of volume limited samples and on the LF and morphology fraction are found to be very important. (abridged)

The Nuclear to Host Galaxy Relation of High‐Redshift Quasars

We present near-infrared imaging with ESO VLT+ISAAC of the host galaxies of low luminosity quasars in the redshift range 1 < z < 2, aimed at investigating the relationship between the nuclear and host galaxy luminosities at high redshift. This work complements our previous study to trace the cosmological evolution of the host galaxies of high luminosity quasars (Falomo et al. 2004). The new sample includes 15 low luminosity quasars, nine radio-loud (RLQ) and six radio-quiet (RQQ). They have similar distribution of redshift and optical luminosity, and together with the high luminosity quasars they cover a large range (~4 mag) of the quasar luminosity function. The host galaxies of both types of quasars are in the range of massive inactive ellipticals between L* and 10 L*. RLQ hosts are systematically more luminous than RQQ hosts by a factor of ~2. This difference is similar to that found for the high luminosity quasars. This luminosity gap appears to be independent of the rest-frame U-band luminosity but clearly correlated with the rest-frame R-band luminosity. The color difference between the RQQs and the RLQs is likely a combination of an intrinsic difference in the strength of the thermal and nonthermal components in the SEDs of RLQs and RQQs, and a selection effect due to internal dust extinction. For the combined set of quasars, we find a reasonable correlation between the nuclear and the host luminosities. This correlation is less apparent for RQQs than for RLQs. If the R-band luminosity is representative of the bolometric luminosity, and assuming that the host luminosity is proportional to the black hole mass, as observed in nearby massive spheroids, quasars emit with a relatively narrow range of power with respect to their Eddington luminosity and with the same distribution for RLQs and RQQs.

An extreme rotation measure in the high-redshift radio galaxy PKS B0529-549

We present the results of a radio polarimetric study of the high-redshift radio galaxy PKS B0529-549 (z=2.575), based on high-resolution 12 mm and 3 cm images obtained with the Australia Telescope Compact Array (ATCA). The source is found to have a rest-frame Faraday rotation measure of -9600 rad m^{-2}, the largest seen thus far in the environment of a z > 2 radio galaxy. In addition, the rest-frame Faraday dispersion in the screen responsible for the rotation is calculated to be 5800 rad m^{-2}, implying rotation measures as large as -15400 rad m^{-2}. Using supporting near-IR imaging from the Very Large Telescope (VLT), we suggest that the rotation measure originates in the Ly-alpha halo surrounding the host galaxy, and estimate the magnetic field strength to be ~10 microGauss. We also present a new optical spectrum of PKS B0529-549 obtained with the New Technology Telescope (NTT), and propose that the emission-line ratios are best described by a photoionization model. Furthermore, the host galaxy is found to exhibit both hot dust emission at 8.0 microns and significant internal visual extinction (~1.6 mag), as inferred from Spitzer Space Telescope near/mid-IR imaging.

Optical and NIR spectroscopy of Mrk 1210: constraints and physical conditions of the active nucleus

Near-infrared and optical spectroscopy of the nuclear and extended emission region of the Seyfert2 galaxy Mrk1210 is presented. This galaxy is outstanding because it displays signatures of recent circumnuclear star formation and a high-level of X-ray activity, in addition to the classical spectral characteristics typical of an AGN. The NIR nuclear spectrum, which covers the interval 0.8-2.4 microns, is dominated by HI and HeI recombination lines as well a [SII], [SIII] and [Fe II] forbidden lines. Coronal lines of [SVIII], [SIX], [SiVI], [SiX], and [CaVIII] in addition to molecular H_2 lines are also detected. An estimate of the contribution of the stellar population to the continuum is made by means of the ^{12}CO(6-3) 1.618 microns overtone bandhead. It was found that 83% of the H-band continuum is of stellar origin. It improves previous estimates, which claimed that at least 50% of the observed continuum was attributed to the AGN. The analysis of the emission line profiles, both allowed and forbidden, shows a narrower line on top of a broad blue-shifted component. The latter seems to be associated to a nuclear outflow. This result does not required the presence of a hidden BLR claimed to be present in previous NIR observations of this object. Internal extinction, calculated by means of several indicators including [FeII] flux ratios not previously used before in AGNs, reveals a dusty AGN, while the extended regions are little or not affected by dust. Density and temperature for the NLR are calculated using optical and NIR lines diagnostic ratios. The results show temperatures from 10000K up to 40000K and densities between 10^3-10^5 cm^{-3}. The larger temperatures points out that shocks must contribute to the line emission.

Properties of luminous red galaxies in the Sloan Digital Sky Survey

We perform population-synthesis modelling of a magnitude-limited sample of 4391 luminous red galaxies selected from the Sloan Digital Sky Survey Data Release 4 (SDSS DR4). We fit measured spectral indices using a large library of high-resolution spectra, covering a wide range of metallicities and assuming an exponentially decaying star formation rate punctuated by bursts, to obtain median-likelihood estimates for the light-weighted age, metallicity, stellar mass and internal extinction for the galaxies. The ages lie predominantly in the range 4-10 Gyr, peaking near 6 Gyr, with metallicities in the range -0.4 < [Z/H] < 0.4, peaking at [Z/H] ≈0.2. Only a few per cent of the spectra are better fitted allowing for a burst in addition to continuous star formation. For these systems, typically one-quarter to one-third of the stars are formed in the burst. The total stellar masses of all the galaxies are confined to a very narrow range around ∼3 x 10 11 M ⊙ , consistent with the expected homogeneity of the sample. Our results broadly agree with those of previous groups using an independent population-synthesis code. We find, however, that our choice in priors results in ages 1-2 Gyr smaller, decreasing the peak formation epoch from about z=2.3 to 1.3 for the stars. To describe the distribution in measured mean metallicity of the galaxies, we develop a metal evolution model incorporating stochastic star formation quenching motivated by recent attempts to account for the apparent 'antihierarchical' formation of elliptical galaxies. Two scenarios emerge, a closed box with an effective stellar yield of 0.26, and an accreting box with an effective stellar yield of 0.10. Both scenarios require an initial mass function weighted towards massive stars. They also require characteristic star formation quenching times of about 10 8 yr, the expected lifetime of luminous quasi-stellar objects. The models predict an anticorrelation between the age and mean metallicity of the galaxies similar to that observed.

A possible interrelation between the estimated luminosity distances and internal extinctions of type Ia supernovae

We studied the statistical properties of the luminosity distance and internal extinction data of type Ia supernovae in the lists published by Tonry et al. (2003) and Barris et al. (2004). After selecting the luminosity distance in an empty Universe as a reference level we divided the sample into low z < 0.25 and high z ≥ 0.25 parts. We further divided these subsamples by the median of the internal extinction. Performing sign tests using the standardized residuals between the estimated logarithmic luminosity distances and those of an empty universe, on the four subsamples separately, we recognized that the residuals were distributed symmetrically in the low redshift region, independently from the internal extinction. On the contrary, the low extinction part of the data of z ≥ 0.25 clearly showed an excess of the points with respect to an empty Universe which was not the case in the high extinction region. This diversity pointed to an interrelation between the estimated luminosity distance and internal extinction. To characterize quantitatively this interrelation we introduced a hidden variable making use of the technics of factor analysis. After subtracting that part of the residual which was explained by the hidden variable we obtained luminosity distances which were already free from interrelation with internal extinction. Fitting the corrected luminosity distances with cosmological models we concluded that the SN Ia data alone did not exclude the possibility of the Λ = 0 solution. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Integral Field Spectroscopy of the Luminous Infrared Galaxy Arp 299 (IC 694 + NGC 3690)

The luminous infrared galaxy Arp 299 (IC 694 + NGC 3690) is studied using optical integral field spectroscopy obtained with the INTEGRAL system, together with archival Hubble Space Telescope WFPC2 and NICMOS images. The stellar and ionized gas morphology shows λ-dependent variations due to the combined effects of the dust internal extinction and the nature and spatial distribution of the different ionizing sources. The two-dimensional ionization maps have revealed an off-nuclear conical structure of about 4 kpc in length, characterized by high-excitation conditions and a radial gradient in the gas electron density. The apex of this structure coincides with B 1 region of NGC 3690, which in turn presents Seyfert-like ionization, high extinction, and a high velocity dispersion. These results strongly support the hypothesis that B1 is the true nucleus of NGC 3690, where an AGN is located. In the circumnuclear regions H II-like ionization dominates, while LINER-like ionization is found elsewhere. The Hα-emitting sources with ages from 3.3 to 7.2 × 106 yr, have masses of between 6 and 680 × 106 M⊙; and contribute about 45% to the bolometric luminosity (extinction corrected). The ionized (Hα) and neutral (Na D) gas velocity fields show similar structure on scales of several hundred to about 1 kpc, indicating that these gas components are kinematically coupled. The kinematic structure is complex and on scales of about 0.2 kpc does not appear to be dominated by the presence of ordered, rotational motions. The large velocity dispersion measured in NGC 3690 indicates that this galaxy is the most massive of the system. The low velocity amplitude and dispersion of the interface suggest that the ionized gas is slowly rotating or in a close to quiescent phase. © 2006. The American Astronomical Society. All rights reserved.

The Survey for Ionization in Neutral Gas Galaxies. II. The Star Formation Rate Density of the Local Universe

We derive observed Halpha and R band luminosity densities of an HI-selected sample of nearby galaxies using the SINGG sample to be l_Halpha' = (9.4 +/- 1.8)e38 h_70 erg s^-1 Mpc^-3 for Halpha and l_R' = (4.4 +/- 0.7)e37 h_70 erg s^-1 A^-1 Mpc^-3 in the R band. This R band luminosity density is approximately 70% of that found by the Sloan Digital Sky Survey. This leads to a local star formation rate density of log(SFRD) = -1.80 +0.13/-0.07(random) +/- 0.03(systematic) + log(h_70) after applying a mean internal extinction correction of 0.82 magnitudes. The gas cycling time of this sample is found to be t_gas = 7.5 +1.3/-2.1 Gyr, and the volume-averaged equivalent width of the SINGG galaxies is EW(Halpha) = 28.8 +7.2/-4.7 A (21.2 +4.2/-3.5 A without internal dust correction). As with similar surveys, these results imply that SFRD(z) decreases drastically from z ~ 1.5 to the present. A comparison of the dynamical masses of the SINGG galaxies evaluated at their optical limits with their stellar and HI masses shows significant evidence of downsizing: the most massive galaxies have a larger fraction of their mass locked up in stars compared with HI, while the opposite is true for less massive galaxies. We show that the application of the Kennicutt star formation law to a galaxy having the median orbital time at the optical limit of this sample results in a star formation rate decay with cosmic time similar to that given by the SFRD(z) evolution. This implies that the SFRD(z) evolution is primarily due to the secular evolution of galaxies, rather than interactions or mergers. This is consistent with the morphologies predominantly seen in the SINGG sample.

Massive and Evolved Galaxies at z ≥ 5

AbstractWe search for massive and evolved galaxies at z ≥ 5 in the Great Observatories Origins Deep Survey (GOODS) southern field. Combining HST ACS, VLT ISAAC and Spitzer IRAC broad–band photometric data, we develop a color selection technique to identify candidates for being evolved galaxies at high redshifts. The color selection is primarily based on locating the Balmer–break using the K- and 3.6 μm bands. Stellar population synthesis models are fitted to the SEDs of these galaxies to identify the final sample. We find 11 candidates with photometric redshifts in the range 4.9 &lt; z &lt; 5.6, dominated by an old stellar population, with ages 0.2-1.0 Gyr, and stellar masses in the range (0.7 − 5) × 1011 M⊙. Most of the candidates have modest amounts of internal dust extinction. The majority of the stars in these galaxies were formed at z&gt;9 and the current star formation activity is a few percent of the inferred initial star formation rate.

Rest‐Frame Optical Spectroscopic Classifications for Submillimeter Galaxies

We report the results of a systematic near-IR spectroscopic survey using the Subaru, VLT, and Keck Telescopes of a sample of high-redshift ULIRGs mainly composed of submillimeter-selected galaxies. Our observations span the rest-frame optical range containing nebular emission lines such as Hβ, [O III] λλ4959, 5007, and [O II] λ3727, which are essential for making robust diagnostics of the physical properties. Using the Hα/Hβ emission line ratios, we derive internal extinction estimates for these galaxies similar to those of local ULIRGs: A_V ~ 2.9 ± 0.5. Correcting the Hα estimates of the star formation rate for dust extinction results in rates that are consistent with those estimated from the far-IR luminosity. The majority (>60%) of our sample show spectral features characteristic of AGNs (although this partially reflects an observational bias), with ~65% exhibiting broad Balmer emission lines. A proportion of these sources show relatively low [O III] λ5007/Hβ line ratios, which are similar to those of narrow-line Seyfert 1 galaxies, suggesting low-mass black holes that are rapidly growing. In the subsample of our survey with both [O III] λ5007 and hard X-ray coverage, at least ~60% show an excess of [O III] λ5007 emission, by a factor of 5-10, relative to the hard X-ray luminosity compared to the correlation between these two properties seen in Seyfert galaxies and QSOs locally. From our spectral diagnostics, we propose that the strong [O III] λ5007 emission in these galaxies arises from shocks in dense gaseous regions. Due to sensitivity and resolution limits, our sample is biased to strong-line emitters and hence our results do not yet provide a complete view of the physical properties of the whole high-redshift ULIRG population.

Clusters at Half Hubble Time: Galaxy Structure and Colors in RX J0152.7−1357 and MS 1054−03

We study the photometric and structural properties of spectroscopically confirmed members in the two massive X-ray‐selected z ≈ 0.83 galaxy clusters MS 1054‐03 and RX J0152.7‐1357 using three-band mosaic imaging with the Hubble Space TelescopeAdvanced Camera for Surveys. The samples include 105 and 140 members of RX J0152.7‐1357 and MS 1054‐03, respectively, with ACS F775W magnitude i775 < 24.0. We fit the 2-D galaxy light profiles to determine effective radii and Se rsic indices; deviations from the smooth profiles are quantified by the ratio of the rms residuals to the mean of t he galaxy model. Galaxies are then classified according to a combination of this rms/mean ratio and the Sersic index; the resulting classes correlate well with visually classified morphological types, but are less affec ted by orientation. We find the size‐surface brightness relations in the two clusters to be very similar, supporting recent results on the evolution of this relationship with redshift. We examine in detail the color‐magnitude relations in these clusters and systematic effects on the residuals with respect to these relations. The color-ma gnitude residuals correlate with the local density, as measured from both galaxy numbers and weak lensing. These correlations are strongest for the full galaxy samples (commensurate with the morphology‐density relation), but are also present at lower significance levels for the early- and late-type samples individually. Weaker correlations are found with cluster radius, resulting from the more fundamental dependence on local density. We identify a threshold surface mass density of � ≈ 0.1, in units of the critical density, above which there are rel atively few blue (star-forming) galaxies. In RX J0152.7‐1357, there is an offset of 0.006 ± 0.002 in the mean redshifts of the early- and late-type galaxies, which produces a trend in the color residuals with velocity and may result from an infalling foreground association of late-type galaxies. Comparison of the color‐color diagrams for these clusters to stellar population models implies that a range of star formation time-scales are needed to reproduce the locus of galaxy colors. We also identify two galaxies, one in each cluster, whose colors can only be explained by large amounts, AV ∼ 1 mag, of internal dust extinction. Converting to rest-frame bandpasses, we find elliptical galaxy color scatters of 0.03 ± 0.01 mag in (U-B) and 0.07 ± 0.01 mag in (U-V), indicating mean ages of ∼ 3.5 Gyr, similar to the estimates from the mean colors and corresponding to formation at z ≈ 2.2. Thus, when the universe was half its present age, cluster ellipticals were half the age of the universe at that epoch; the same is coincidentally true of the median ages of ellipticals today. However, the most massive local cluster ellipticals have ages & 10 Gyr, consistent with our results for their likely progenitors at z & 0.8.

Stellar Populations in the Nuclei of Late‐Type Spiral Galaxies

(Abridged) As part of an ongoing effort to study the stellar nuclei of very late-type, bulge-less spirals, we present results from a high-resolution spectroscopic survey of nine such nuclear star clusters, undertaken with VLT/UVES. We fit the spectra with population synthesis models and measure Lick-type indices to determine mean luminosity-weighted ages, which range from 4.1*10^7 to 1.1*10^10 years and are insensitive to assumed metallicity or internal extinction. The average metallicity of nuclear clusters in late-type spirals is slightly sub-solar (<Z> = 0.015) but shows significant scatter. The fits also show that the nuclear cluster spectra are best described by a mix of several generations of stars. This is supported by the fact that only models with composite stellar populations yield mass-to-light ratios that match those obtained from dynamical measurements. The last star formation episode was on average 34 Myr ago, while all clusters experienced some star formation in the last 100 Myr. We thus conclude that the nuclear clusters undergo repeated episodes of star formation. The robustness with respect to possible contamination from the underlying galaxy disk is demonstrated by comparison to spectra obtained with HST/STIS. Combining these results with those from Walcher et al. (2005), we have thus shown that the stellar nuclei of these bulge-less galaxies are massive and dense star clusters that form stars recurrently until the present day. This unique set of properties is likely due to the central location of these clusters in their host galaxies.

The short-duration GRB 050724 host galaxy in the context of the long-duration GRB hosts

We report optical and near-infrared broad band observations of the short-duration GRB 050724 host galaxy, used to construct its spectral energy distribution (SED). Unlike the hosts of long-duration gamma-ray bursts (GRBs), which show younger stellar populations, the SED of the GRB 050724 host galaxy is optimally fitted with a synthetic elliptical galaxy template based on an evolved stellar population (age ~2.6 Gyr). The SED of the host is difficult to reproduce with non-evolving metallicity templates. In contrast, if the short GRB host galaxy metallicity enrichment is considered, the synthetic templates fit the observed SED satisfactorily. The internal host extinction is low (A_v \~< 0.4 mag) so it cannot explain the faintness of the afterglow. This short GRB host galaxy is more massive (~5x10^10 Mo) and luminous (~1.1 L*) than most of the long-duration GRB hosts. A statistical comparison based on the ages of short- and long-duration GRB host galaxies strongly suggests that short-duration GRB hosts contain, on average, older progenitors. These findings support a different origin for short- and long-duration GRBs.

Investigating the Andromeda stream — I. Simple analytic bulge—disc—halo model for M31

This paper is the first in a series which studies interactions between M31 and its satellites, including the origin of the giant southern stream. We construct accurate yet simple analytic models for the potential of the M31 galaxy to provide an easy basis for the calculation of orbits in M31's halo. We use a Navarro, Frenk and White (NFW) dark halo, an exponential disc, a Hernquist bulge, and a central black hole point mass to describe the galaxy potential. We constrain the parameters of these functions by comparing to existing surface-brightness, velocity-dispersion, and rotation-curve measurements of M31. Our description provides a good fit to the observations, and agrees well with more sophisticated modelling of M31. While in many respects the parameter set is well constrained, there is substantial uncertainty in the outer halo potential and a near-degeneracy between the disc and halo components, producing a large, nearly two-dimensional allowed region in parameter space. We limit the allowed region using theoretical expectations for the halo concentration, baryonic content, and stellar mass-to-light ratio (M/L R ), finding a smaller region where the parameters are physically plausible. Our proposed mass model for M31 has M bulge = 3.2 x 10 10 M ⊙ , M disc = 7.2 x 10 10 M ⊙ , and M 200 = 7.1 x 10 11 M ⊙ , with uncorrected (for internal and foreground extinction) mass-to-light ratios of M/L R = 3.9 and 3.3 for the bulge and disc, respectively. We present some illustrative test-particle orbits for the progenitor of the stellar stream in our galaxy potential, highlighting the effects of the remaining uncertainty in the disc and halo masses.

LARGE-ACTIVATION-ENERGY ASYMPTOTIC ANALYSIS OF MULTICOMPONENT-FUEL DIFFUSION FLAMES

ABSTRACT This analysis addresses some aspects of the internal structure and extinction of diffusion flames established by burning of multicomponent fuel (n-heptane diffusion flame enriched with hydrogen). By presuming one-global-step reactions with large activation energy, the zone where all reactions take place is described by large-activation-energy asymptotics. In this study, it is also supposed that the values of the Damköhler numbers for the reactions are very close and the values of the activation energies are also very close. Under these conditions, all reactions will be performed inside the same region. The results show that the reaction with small Damköhler number and/or large activation energy controls the extinction of the multicomponent-fuel diffusion flame. Under the condition of equal Damköhler numbers and equal activation energies, Hamins and Seshadri's (Hamins, A. and Seshadri, K. (1984b) Proc. Combust. Instit., 20, 1905–1913) results are recovered.

On the nature of nearby GRB/SN host galaxies

We present and discuss optical diagnostics of the low redshift ( z < 0.2) galaxies that are known to have hosted supernovae associated with γ-ray bursts (GRBs). The three galaxies are all actively star forming sub-luminous ( L < L ⋆) galaxies with relatively low metallicities ( Z ≲ Z ⊙). We find no evidence for substantial internal extinction within any of the galaxies. We derive star formation rates (SFR) based on Hα luminosities, as well as specific star formation rates (SSFR, star formation rate per unit luminosity). For GRB 980425 (SN 1998bw) we use photometry of the supernova environment to estimate the mass of the progentitor to ≳30 M ⊙. These three host galaxies have global properties (luminosities, SFR, SSFR, metallicity, colour, reddening) that resemble those of more distant GRB host galaxies. We also compare the host galaxies with a sample of Blue Compact Galaxies (BCGs) in the local universe, and show that these samples have similar properties.

The Host Galaxies of High-Redshift Type Ia Supernovae

SummaryWe present new results on the Hubble diagram of distant type Ia supernovae (SNe Ia) segregated according to the type of host galaxy. This makes it possible to check earlier evidence for a cosmological constant by explicitly comparing SNe residing in galaxies likely to contain negligible dust with the larger sample. The cosmological parameters derived from these SNe Ia hosted by presumed dust-free early-type galaxies support earlier claims for a cosmological constant, which we demonstrate at ≃ 5σ significance, and the internal extinction implied is small even for late-type systems (AB &lt; 0.2). Furthermore, the scatter observed in the SNe Ia Hubble diagrams correlates closely with host galaxy morphology. We find this scatter is smallest for SNe Ia occurring in early-type hosts and largest for those in late-type galaxies. Moreover, SNe residing in late-type hosts appear fainter in their light-curve-width-corrected luminosity than those in early-type hosts, as expected if a modest amount of dust extinction is a contributing factor. Thus, our data demonstrate that host galaxy extinction is unlikely to systematically dim distant SNe Ia in a manner that would produce a spurious cosmological constant.

The Planetary Nebula System of M33

We report the results of a photometric and spectroscopic survey for planetary nebulae (PNs) over the entire body of the Local Group spiral galaxy M33. We use our sample of 152 PNs to show that the bright end of the galaxy's [O III] λ5007 planetary nebula luminosity function (PNLF) has the same sharp cutoff seen in other galaxies. The apparent magnitude of this cutoff, along with the IRAS DIRBE foreground extinction estimate of E(B - V) = 0.041, implies a distance modulus for the galaxy of (m - M)0 = 24.86 (0.94 Mpc). Although this value is ~15% larger than the galaxy's Cepheid distance, the discrepancy likely arises from differing assumptions about the system's internal extinction. Our photometry, which extends more than 3 mag down the PNLF, also reveals that the faint end of M33's PNLF is nonmonotonic, with an inflection point ~2 mag below the PNLF's bright limit. We argue that this feature is due to the galaxy's large population of high core mass planetaries and that its amplitude may eventually be a useful diagnostic for studies of stellar populations. Fiber-coupled spectroscopy of 140 of the PN candidates confirms that M33's PN population rotates along with the old disk, with a small asymmetric drift of ~10 km s-1. Remarkably, the population's line-of-sight velocity dispersion varies little over ~4 optical disk scale lengths, with σrad ~ 20 km s-1. We show that this is due to a combination of factors, including a decline in the radial component of the velocity ellipsoid at small galactocentric radii and a gradient in the ratio of the vertical to radial velocity dispersion. We use our data to derive the dynamical scale length of M33's disk and the disk's mass-to-light ratio. Our most likely solution suggests that the surface mass density of M33's disk decreases exponentially, but with a scale length that is ~2.3 times larger than that of the system's IR luminosity. The large scale length also implies that the disk's V-band mass-to-light ratio changes from M/LV ~ 0.3 in the galaxy's inner regions to M/LV ~ 2.0 at ~9 kpc. Models in which the dark matter is distributed in the plane of the galaxy are excluded by our data.

UV star-formation rates of GRB host galaxies

We study a magnitude-limited sample of 10 gamma-ray burst (GRB) host galaxies with known spectroscopic redshifts (0.43 < z < 2.04). From an analysis of the spectral energy distributions (SEDs), based on published broad-band optical and near-infrared photometry, we derive photometric redshifts, galaxy types, ages of the dominant stellar populations, internal extinctions, and ultraviolet (UV) star-formation rates (SFRs) of the host galaxies. The photometric redshifts are quite accurate despite the heterogeneous nature of the sample: The r.m.s. errors are sigma(z) = 0.21 and sigma(Delta z/(1+z_spec)) = 0.16 with no significant systematic offsets. All the host galaxies have SEDs similar to young starburst galaxies with moderate to low extinction. A comparison of specific SFRs with those of high-redshift galaxies in the Hubble Deep Fields shows that GRB hosts are most likely similar to the field galaxies with the largest specific SFRs. On the other hand, GRB hosts are not significantly younger than starburst field galaxies at similar redshifts, but are found to be younger than a sample of all types of field galaxies.

Multicolor CCD photometry of the dusty, giant, late-type spiral galaxy NGC 5351

The paper reports the results of BV RI surface photometry of the giant galaxy NGC 5351 based on CCD observations obtained on the 1-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. Analysis of the structure and radial brightness distribution in the galaxy shows that NGC 5351 has a complex and, in some places, asymmetric structure. The galaxy possesses a large quantity of dust. The average internal extinction due to dust is AV=1.2m±0.4m. After correcting for the effect of this dust, the parameters of the galaxy are typical of late-type spirals. The compositions of the stellar population in various parts of the galaxy are estimated using two-color diagrams. Star-forming regions in NGC 5351 are identified and studied. Most of the star-forming regions are located in the ring of the galaxy. Evolutionary modeling is used to estimate the ages of regions of violent star formation. An elliptical companion galaxy to NGC 5351 was found. The rotation curve of the galaxy is modeled and its mass estimated. The disk of NGC 5351 is self-gravitating within its optical radius.