13 research outputs found
An Empirical Connection between the UV Color of Early Type Galaxies and the Stellar Initial Mass Function
Using new UV magnitudes for a sample of early-type galaxies, ETGs, with
published stellar mass-to-light ratios, Upsilon_*, we find a correlation
between UV color and Upsilon_* that is tighter than those previously identified
between Upsilon_* and either the central stellar velocity dispersion,
metallicity, or alpha enhancement. The sense of the correlation is that
galaxies with larger Upsilon_* are bluer in the UV. We conjecture that
differences in the lower mass end of the stellar initial mass function, IMF,
are related to the nature of the extreme horizontal branch populations that are
generally responsible for the UV flux in ETGs. If so, then UV color can be used
to identify ETGs with particular IMF properties and to estimate Upsilon_*.Comment: Submitted for publication in ApJ Letter
The connection between the UV colour of early type galaxies and the stellar initial mass function revisited
We extend our initial study of the connection between the UV colour of
galaxies and both the inferred stellar mass-to-light ratio, , and a
mass-to-light ratio referenced to Salpeter initial mass function (IMF) models
of the same age and metallicity, , using new UV
magnitude measurements for a much larger sample of early-type galaxies, ETGs,
with dynamically determined mass-to-light ratios. We confirm the principal
empirical finding of our first study, a strong correlation between the GALEX
FUV-NUV colour and . We show that this finding is not the result of
spectral distortions limited to a single passband (eg. metallicity-dependent
line-blanketing in the NUV band), or of the analysis methodology used to
measure , or of the inclusion or exclusion of the correction for
stellar population effects as accounted for using .
The sense of the correlation is that galaxies with larger , or
larger , are bluer in the UV. We conjecture that
differences in the low mass end of the stellar initial mass function, IMF, are
related to the nature of the extreme horizontal branch stars generally
responsible for the UV flux in ETGs. If so, then UV color can be used to
identify ETGs with particular IMF properties and to estimate . We
also demonstrate that UV colour can be used to decrease the scatter about the
Fundamental Plane and Manifold, and to select peculiar galaxies for follow-up
with which to further explore the cause of variations in and UV
colour.Comment: Accepted for publication in MNRAS, 8 page
The (black hole mass)-(color) relations for early- and late-type galaxies: red and blue sequences
[Abridged] Tight correlations between supermassive black hole (SMBH) mass
() and the properties of the host galaxy have useful implications
for our understanding of the growth of SMBHs and evolution of galaxies. Here,
we present newly observed correlations between and the host galaxy
total UV [3.6] color (, Pearson's r = )
for a sample of 67 galaxies (20 early-type galaxies and 47 late-type galaxies)
with directly measured in the GALEX/SG survey. The colors
are carefully measured in a homogeneous manner using the galaxies' FUV, NUV and
3.6 \micron magnitudes and their multi-component structural decompositions in
the literature. We find that more massive SMBHs are hosted by (early- and
late-type) galaxies with redder colors, but the relations for the two morphological types have slopes that differ at
level. Early-type galaxies define a red sequence in the diagrams, while late-type galaxies trace a blue
sequence. Within the assumption that the specific star formation rate of a
galaxy (sSFR) is well traced by , it follows that the
SMBH masses for late-type galaxies exhibit a steeper dependence on sSFR than
those for early-type galaxies. The and
relations for the sample galaxies reveal a
comparable level of vertical scatter in the log direction, roughly
more than the vertical scatter of the relation.
Our relations suggest different channels
of SMBH growth for early- and late-type galaxies, consistent with their
distinct formation and evolution scenarios.Comment: 27 pages, 8 figures, 6 tables, accepted for publication in Ap
The distribution of star formation in galactic bars as seen with H and stacked GALEX UV imaging
We investigate the spatial distribution of star formation (SF) within bars of
nearby disk galaxies (inclination ) from the SG survey. We
use archival GALEX far- and near-UV imaging for 772 barred galaxies. We also
assemble a compilation of continuum-subtracted H images for 433 barred
galaxies, of which 70 are produced by ourselves from ancillary photometry and
MUSE/CALIFA IFU data cubes. We employ two complementary approaches: i) the
analysis of bar/disk stacks built from co-added UV images of hundreds of
galaxies; and ii) the classification of the morphology of ionised regions in
galaxies into three main SF classes: A) only circumnuclear SF, B) SF at the bar
ends, but not along the bar, and C) SF along the bar. Lenticular galaxies
typically belong to SF class A: this is probably related to bar-induced SF
quenching. The distribution of SF class B peaks for early- and
intermediate-type spirals: this most likely results from the interplay of gas
flow, shocks, and enhanced shear in centrally concentrated galaxies with large
bar amplitudes. Late-type galaxies are mainly assigned to SF class C: we argue
that this is a consequence of low shear. In bar stacks of spirals, the UV
emission traces the stellar bars and dominates on their leading side, as
witnessed in simulations. For early-types, the central UV emission is 0.5
mag brighter in strongly barred galaxies, relative to their weakly barred
counterparts: this is related to the efficiency of strong bars sweeping the
disk gas and triggering central starbursts. We also show that the distributions
of SF in inner ringed galaxies are broadly the same in barred and non-barred
galaxies, including a UV/H deficit in the middle part of the bar: this
hints at the effect of resonance rings trapping gas. Distinct distributions of
SF within bars are reported in galaxies of different morphological types
(Abridged).Comment: Accepted for publication in A&A (September 2, 2020). 18 pages, 14
figures, 2 tables, plus appendices (16 pages, 8 figures, 1 table
Discovery of New Dwarf Galaxy near The Isolated Spiral Galaxy NGC 6503
We report the discovery of a new dwarf galaxy (NGC6503-d1) during the Subaru
extended ultraviolet (XUV) disk survey. It is a likely companion of the spiral
galaxy NGC6503. The resolved images, in B, V, R, i, and Halpha, show an
irregular appearance due to bright stars with underlying, smooth and unresolved
stellar emission. It is classified as the transition type (dIrr/dSph). Its
structural properties are similar to those of the dwarfs in the Local Group,
with a V absolute magnitude ~ -10.5, half-light radius ~400 pc, and central
surface brightness ~25.2. Despite the low stellar surface brightness
environment, one HII region was detected, though its Halpha luminosity is low,
indicating an absence of any appreciable O-stars at the current epoch. The
presence of multiple stellar populations is indicated by the color-magnitude
diagram of ~300 bright resolved stars and the total colors of the dwarf, with
the majority of its total stellar mass ~4x10^6 Msun in an old stellar
population.Comment: Published in ApJL (ApJ, 802, L24). 7 pages, 4 figure
The GALEX/S4G UV-IR color-color diagram: Catching spiral galaxies away from the Blue Sequence
We obtained GALEX FUV, NUV, and Spitzer/IRAC 3.6m photometry for > 2000
galaxies, available for 90% of the S4G sample. We find a very tight "GALEX Blue
Sequence (GBS)" in the (FUV-NUV) versus (NUV-[3.6]) color-color diagram which
is populated by irregular and spiral galaxies, and is mainly driven by changes
in the formation timescale () and a degeneracy between and dust
reddening. The tightness of the GBS provides an unprecedented way of
identifying star-forming galaxies and objects that are just evolving to (or
from) what we call the "GALEX Green Valley (GGV)". At the red end of the GBS,
at (NUV-[3.6]) > 5, we find a wider "GALEX Red Sequence (GRS)" mostly populated
by E/S0 galaxies that has a perpendicular slope to that of the GBS and of the
optical red sequence. We find no such dichotomy in terms of stellar mass
(measured by ), since both massive () blue and red sequence galaxies are identified. The type that is
proportionally more often found in the GGV are the S0-Sa's and most of these
are located in high-density environments. We discuss evolutionary models of
galaxies that show a rapid transition from the blue to the red sequence on
timescale of years.Comment: 7 pages, 4 figures, 1 table. Accepted for publication in ApJ
The GALEX/S(4)G Surface Brightness and Color Profiles Catalog. I. Surface Photometry and Color Gradients of Galaxies
We present new spatially resolved surface photometry in the far-ultraviolet (FUV) and near-ultraviolet (NUV) from images obtained by the Galaxy Evolution Explorer (GALEX) and IRAC1 (3.6 mu m) photometry from the Spitzer Survey of Stellar Structure in Galaxies (S(4)G). We analyze the radial surface brightness profiles mu(FUV), mu(NUV), and mu[3.6], as well as the radial profiles of (FUV - NUV), (NUV -[3.6]), and (FUV -[3.6]) colors in 1931 nearby galaxies (z < 0.01). The analysis of the 3.6 mu m surface brightness profiles also allows us to separate the bulge and disk components in a quasi-automatic way and to compare their light and color distribution with those predicted by the chemo-spectrophotometric models for the evolution of galaxy disks of Boissier & Prantzos. The exponential disk component is best isolated by setting an inner radial cutoff and an upper surface brightness limit in stellar mass surface density. The best-fitting models to the measured scale length and central surface brightness values yield distributions of spin and circular velocity within a factor of two of those obtained via direct kinematic measurements. We find that at a surface brightness fainter than mu([3.6]) = 20.89 mag arcsec(-2), or below 3 x 10(8) M-circle dot kpc(-2) in stellar mass surface density, the average specific star formation rate (sSFR) for star-forming and quiescent galaxies remains relatively flat with radius. However, a large fraction of GALEX Green Valley galaxies show a radial decrease in sSFR. This behavior suggests that an outside-in damping mechanism, possibly related to environmental effects, could be testimony of an early evolution of galaxies from the blue sequence of star-forming galaxies toward the red sequence of quiescent galaxies
The spitzer survey of stellar structure in galaxies (S^4G): stelar masses, sizes, and radial profiles for 2352 nearby galaxies
© 2015. The American Astronomical Society. ArtÃculo firmado por 28 autores.
The authors are grateful to the entire S4G team for their collective effort in this project. We also thank the staff at IRSA, and in particular Justin Howell, for implementing the online access to our data. We acknowledge useful suggestions from an anonymous referee, which helped to improve the scientific content of this paper. We thank Rebecca Lange for sharing the contour data of the GAMA mass–size relation.
J.C.M.M. acknowledges the receipt of an ESO Fellowship. This work was also co-funded by NASA JPL/Spitzer grant RSA 1374189 provided for the S(^4)G project. J.C.M.M., K.S., and T.K. also acknowledge support from the NRAO. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. We also acknowledge financial support from the DAGAL network from the People Programme (Marie Curie Actions) of the European Unions Seventh Framework Programme FP7/2007-2013/under REA grant agreement number PITN-GA-2011-289313. E.A. and A.B. also acknowledge financial support from the CNES (Centre National d'Etudes Spatiales-France). J.H.K. and A.G.d.P. acknowledge financial support from the Spanish MINECO under grants number AYA2013-41243-P and AYA2012-30717, respectively.The Spitzer Survey of Stellar Structure in Galaxies is a volume, magnitude, and size-limited survey of 2352 nearby galaxies with deep imaging at 3.6 and 4.5 μm. In this paper, we describe our surface photometry pipeline and showcase the associated data products that we have released to the community. We also identify the physical mechanisms leading to different levels of central stellar mass concentration for galaxies with the same total stellar mass. Finally, we derive the local stellar mass-size relation at 3.6 μm for galaxies of different morphologies. Our radial profiles reach stellar mass surface densities below ∼1 M_⨀ pc^-2. Given the negligible impact of dust and the almost constant mass-to-light ratio at these wavelengths, these profiles constitute an accurate inventory of the radial distribution of stellar mass in nearby galaxies. From these profiles we have also derived global properties such as asymptotic magnitudes (and the corresponding stellar masses), isophotal sizes and shapes, and concentration indices. These and other data products from our various pipelines (science-ready mosaics, object masks, 2D image decompositions, and stellar mass maps)can be publicly accessed at IRSA (http://irsa.ipac.caltech.edu/data/SPITZER/S4G/).Unión Europea. FP7Ministerio de EconomÃa y Competitividad (MINECO), EspañaSpitzer Space Telescope - Jet Propulsion Laboratory (JPL - California Institute of Technology - NASA)National Radio Astronomy Observatory (NRAO)People Programme (Marie Curie Actions) UECNES (Centre National d'Etudes Spatiales-France)European Southern Observatory (ESO)National Aeronautics and Space Administration (NASA), EE.UU.Depto. de FÃsica de la Tierra y AstrofÃsicaFac. de Ciencias FÃsicasTRUEpu