Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userUV-IR color profiles of the outer regions of 2K nearby S$^{4}$G galaxies
44
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We present our new, spatially-resolved, photometry in FUV and NUV from images obtained by GALEX, and IRAC1 (3.6 $mu$m) photometry obtained by the Spitzer Space Telescope. We analyzed the surface brightness profiles $mu_{rm{FUV}}$, $mu_{rm{NUV}}$, $mu_{[3.6]}$, as well as the radial evolution of the (FUV-NUV), (FUV - [3.6]), and (NUV - [3.6]) colors in the Spitzer Survey of Stellar Structures in Galaxies (S$^{4}$G) galaxies (d$<$40 Mpc) sample. We defined the GALEX Blue Sequence (GBS) and GALEX Red Sequence (GBR) from the (FUV - NUV) versus (NUV - [3.6]) color-color diagram, populated by late-type star forming galaxies and quiescent early-type galaxies respectively. While most disk becomes radially bluer for GBS galaxies, and stay constant for GRS galaxies, a large fraction ($>$50%) of intermediary GALEX Green Valley (GGV) galaxies outer disks are becoming redder. An outside-in quenching mechanism such as environmentally-related mechanisms such as starvation or ram-pressure-stripping could explain our results.
rate research
Read More
We obtained GALEX FUV, NUV, and Spitzer/IRAC 3.6$mu$m photometry for > 2000 galaxies, available for 90% of the S4G sample. We find a very tight GALEX Blue Sequence (GBS) in the (FUV-NUV) versus (NUV-[3.6]) color-color diagram which is populated by irregular and spiral galaxies, and is mainly driven by changes in the formation timescale ($tau$) and a degeneracy between $tau$ 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 $rm{M}_{[3.6]}$), since both massive ($M_{star} > 10^{11} M_{odot}$) blue and red sequence galaxies are identified. The type that is proportionally more often found in the GGV are the S0-Sas 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 $10^{8}$years.
We have explored radial color and stellar surface mass density profiles for a sample of 85 late-type spiral galaxies with deep (down to ~27 mag arcsec^-2) SDSS g- and r-band surface brightness profiles. About 90% of the light profiles have been classified as broken exponentials, exhibiting either truncations (Type II galaxies) or antitruncations (Type III galaxies). The color profiles of Type II galaxies show a U shape with a minimum of (g - r) = 0.47 +- 0.02 mag at the break radius. Around the break radius, Type III galaxies have a plateau region with a color of (g - r) = 0.57 +- 0.02. Using the color to calculate the stellar surface mass density profiles reveals a surprising result. The breaks, well established in the light profiles of the truncated galaxies, are almost gone, and the mass profiles resemble now those of the pure exponential (Type I) galaxies. This result suggests that the origin of the break in Type II galaxies is more likely due to a radial change in stellar population than being associated to an actual drop in the distribution of mass. Type III galaxies, however, seem to preserve their shape in the stellar mass density profiles. We find that the stellar surface mass density at the break for truncated galaxies is 13.6 +- 1.6 Msun pc^-2 and for the antitruncated ones is 9.9 +- 1.3 Msun pc^-2 . We estimate that the fraction of stellar mass outside the break radius is ~15% for truncated galaxies and ~9% for antitruncated galaxies.
Using 3.6 and 4.5$mu$m images of 73 late-type, edge-on galaxies from the S$^4$G survey, we compare the richness of the globular cluster populations of these galaxies to those of early type galaxies that we measured previously. In general, the galaxies presented here fill in the distribution for galaxies with lower stellar mass, M$_*$, specifically $log({rm M}_*/{rm M}_odot) < 10$, overlap the results for early-type galaxies of similar masses, and, by doing so, strengthen the case for a dependence of the number of globular clusters per $10^9 {rm M}_odot$ of galaxy stellar mass, T$_{rm N}$, on M$_*$. For $8.5 < log ({rm M}_*/{rm M}_odot) < 10.5$ we find the relationship can be satisfactorily described as T$_{rm N} = ({rm M}_*/10^{6.7})^{-0.56}$ when M$_*$ is expressed in solar masses. The functional form of the relationship is only weakly constrained and extrapolation outside this range is not advised. Our late-type galaxies, in contrast to our early-types, do not show the tendency for low mass galaxies to split into two T$_{rm N}$ families. Using these results and a galaxy stellar mass function from the literature, we calculate that in a volume limited, local Universe sample, clusters are most likely to be found around fairly massive galaxies (M$_* sim 10^{10.8}$ M$_odot$) and present a fitting function for the volume number density of clusters as a function of parent galaxy stellar mass. We find no correlation between T$_{rm N}$ and large-scale environment, but do find a tendency for galaxies of fixed M$_*$ to have larger T$_{rm N}$ if they have converted a larger proportion of their baryons into stars.
Using 3.6$mu$m images of 97 early-type galaxies, we develop and verify methodology to measure globular cluster populations from the S$^4$G survey images. We find that 1) the ratio, T$_{rm N}$, of the number of clusters, N$_{rm CL}$, to parent galaxy stellar mass, M$_*$, rises weakly with M$_*$ for early-type galaxies with M$_* > 10^{10}$ M$_odot$ when we calculate galaxy masses using a universal stellar initial mass function (IMF), but that the dependence of T$_{rm N}$ on M$_*$ is removed entirely once we correct for the recently uncovered systematic variation of IMF with M$_*$, and 2) for M$_* < 10^{10}$ M$_odot$ there is no trend between N$_{rm CL}$ and M$_*$, the scatter in T$_{rm N}$ is significantly larger (approaching 2 orders of magnitude), and there is evidence to support a previous, independent suggestion of two families of galaxies. The behavior of N$_{rm CL}$ in the lower mass systems is more difficult to measure because these systems are inherently cluster poor, but our results may add to previous evidence that large variations in cluster formation and destruction efficiencies are to be found among low mass galaxies. The average fraction of stellar mass in clusters is $sim$ 0.0014 for M$_* > 10^{10}$ M$_odot$ and can be as large as $sim 0.02$ for less massive galaxies. These are the first results from the S$^4$G sample of galaxies, and will be enhanced by the sample of early-type galaxies now being added to S$^4$G and complemented by the study of later type galaxies within S$^4$G.
The Spitzer Survey of Stellar Structure in Galaxies (S$^4$G, Sheth et. al. 2010) is a deep 3.6 and 4.5 $mu$m imaging survey of 2352 nearby ($< 40$ Mpc) galaxies. We describe the S$^4$G data analysis pipeline 4, which is dedicated to 2-dimensional structural surface brightness decompositions of 3.6 $mu$m images, using GALFIT3.0 citep{peng2010}. Besides automatic 1-component Sersic fits, and 2-component Sersic bulge + exponential disk fits, we present human supervised multi-component decompositions, which include, when judged appropriate, a central point source, bulge, disk, and bar components. Comparison of the fitted parameters indicates that multi-component models are needed to obtain reliable estimates for the bulge Sersic index and bulge-to-total light ratio ($B/T$), confirming earlier results citep{laurikainen2007, gadotti2008, weinzirl2009}. In this first paper, we describe the preparations of input data done for decompositions, give examples of our decomposition strategy, and describe the data products released via IRSA and via our web page ({bf tt www.oulu.fi/astronomy/S4G_PIPELINE4/MAIN}). These products include all the input data and decomposition files in electronic form, making it easy to extend the decompositions to suit specific science purposes. We also provide our IDL-based visualization tools (GALFIDL) developed for displaying/running GALFIT-decompositions, as well as our mask editing procedure (MASK_EDIT) used in data preparation. In the second paper we will present a detailed analysis of the bulge, disk, and bar parameter derived from multi-component decompositions.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
