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Register a new userStellar populations in local star-forming galaxies
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Added by
Pablo G. Perez-Gonzalez
Publication date
2003
fields
Physics
and research's language is
English
Authors
P. G. Perez-Gonzalez
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The main goal of this thesis work is studying the main properties of the stellar populations embedded in a statistically complete sample of local active star-forming galaxies: the Universidad Complutense de Madrid (UCM) Survey of emission-line galaxies. This sample contains 191 local star-forming galaxies at an average redshift of 0.026. The survey was carried out using an objective-prism technique centered at the wavelength of the Halpha nebular emission-line (a common tracer of recent star formation). (continues)
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We present the integrated properties of the stellar populations in the Universidad Complutense de Madrid Survey galaxies. Applying the techniques described in the first paper of this series, we derive ages, burst masses and metallicities of the newly-formed stars in our sample galaxies. The population of young stars is responsible for the Halpha emission used to detect the objects in the UCM Survey. We also infer total stellar masses and star formation rates in a consistent way taking into account the evolutionary history of each galaxy. We find that an average UCM galaxy has a total stellar mass of ~1E10 Msun, of which about 5% has been formed in an instantaneous burst occurred about 5 Myr ago, and sub-solar metallicity. Less than 10% of the sample shows massive starbursts involving more than half of the total mass of the galaxy. Several correlations are found among the derived properties. The burst strength is correlated with the extinction and with the integrated optical colours for galaxies with low obscuration. The current star formation rate is correlated with the gas content. A stellar mass-metallicity relation is also found. Our analysis indicates that the UCM Survey galaxies span a broad range in properties between those of galaxies completely dominated by current/recent star formation and those of normal quiescent spirals. We also find evidence indicating that star-formation in the local universe is dominated by galaxies considerably less massive than L*.
We present the optical and near-infrared luminosity and mass functions of the local star-forming galaxies in the Universidad Complutense de Madrid Survey. A bivariate method which explicitly deals with the Halpha selection of the survey is used when estimating these functions. Total stellar masses have been calculated on a galaxy-by-galaxy basis taking into account differences in star formation histories. The main difference between the luminosity distributions of the UCM sample and the luminosity functions of the local galaxy population is a lower normalization (phi^*), indicating a lower global volume density of UCM galaxies. The typical near-infrared luminosity (L^*) of local star-forming galaxies is fainter than that of normal galaxies. This is a direct consequence of the lower stellar masses of our objects. However, at optical wavelengths (B and r) the luminosity enhancement arising from the young stars leads to M^* values that are similar to those of normal galaxies. The fraction of the total optical and near infrared luminosity density in the local Universe associated with star-forming galaxies is 10-20%. Fitting the total stellar mass function using a Schechter parametrization we obtain alpha=-1.15+/-0.15, log({M}^*)=10.82+/-0.17 Msun and log(phi^*)=-3.04+/-0.20 Mpc^{-3}. This gives an integrated total stellar mass density of 10^{7.83+/-0.07} Msun Mpc^{-3} in local star-forming galaxies (H_0=70 km s^{-1} Mpc^{-1}, Omega_M=0.3, Lambda=0.7). The volume-averaged burst strength of the UCM galaxies is b=0.04+/-0.01, defined as the ratio of the mass density of stars formed in recent bursts (age<10 Myr) to the total stellar mass density in UCM galaxies. Finally, we derive that, in the local Universe, (13+/-3)% of the total baryon mass density in the form of stars is associated with star-forming galaxies.
Stellar population parameters correlate with a range of galaxy properties, but it is unclear which relations are causal and which are the result of another underlying trend. In this series, we quantitatively compare trends between stellar population properties and galaxy structural parameters in order to determine which relations are intrinsically tighter, and are therefore more likely to reflect a causal relation. Specifically, we focus on the galaxy structural parameters of mass $M$, gravitational potential $Phisim M/R_e$, and surface mass density $Sigmasim M/R_e^2$. In Barone et al. (2018) we found that for early-type galaxies the age-$Sigma$ and [Z/H]-$Phi$ relations show the least intrinsic scatter as well as the least residual trend with galaxy size. In this work we study the ages and metallicities measured from full spectral fitting of 2085 star-forming galaxies from the SDSS Legacy Survey, selected so all galaxies in the sample are probed to one effective radius. As with the trends found in early-type galaxies, we find that in star-forming galaxies age correlates best with stellar surface mass density, and [Z/H] correlates best with gravitational potential. We discuss multiple mechanisms that could lead to these scaling relations. For the [Z/H]--$Phi$ relation we conclude that gravitational potential is the primary regulator of metallicity, via its relation to the gas escape velocity. The age--$Sigma$ relation is consistent with compact galaxies forming earlier, as higher gas fractions in the early universe cause old galaxies to form more compactly during their in-situ formation phase, and may be reinforced by compactness-related quenching mechanisms.
We constrain the mass distribution in nearby, star-forming galaxies with the Star Formation Reference Survey (SFRS), a galaxy sample constructed to be representative of all known combinations of star formation rate (SFR), dust temperature, and specific star formation rate (sSFR) that exist in the Local Universe. An innovative two-dimensional bulge/disk decomposition of the 2MASS/$K_{s}$-band images of the SFRS galaxies yields global luminosity and stellar mass functions, along with separate mass functions for their bulges and disks. These accurate mass functions cover the full range from dwarf galaxies to large spirals, and are representative of star-forming galaxies selected based on their infra-red luminosity, unbiased by AGN content and environment. We measure an integrated luminosity density $j$ = 1.72 $pm$ 0.93 $times$ 10$^{9}$ L$_{odot}$ $h^{-1}$ Mpc$^{-3}$ and a total stellar mass density $rho_{M}$ = 4.61 $pm$ 2.40 $times$ 10$^{8}$ M$_{odot}$ $h^{-1}$ Mpc$^{-3}$. While the stellar mass of the emph{average} star-forming galaxy is equally distributed between its sub-components, disks globally dominate the mass density budget by a ratio 4:1 with respect to bulges. In particular, our functions suggest that recent star formation happened primarily in massive systems, where they have yielded a disk stellar mass density larger than that of bulges by more than 1 dex. Our results constitute a reference benchmark for models addressing the assembly of stellar mass on the bulges and disks of local ($z = 0$) star-forming galaxies.
We present $HST$ narrow-band near-infrared imaging of Pa$alpha$ and Pa$beta$ emission of 48 local Luminous Infrared Galaxies (LIRGs) from the Great Observatories All-Sky LIRG Survey (GOALS). These data allow us to measure the properties of 810 spatially resolved star-forming regions (59 nuclei and 751 extra-nuclear clumps), and directly compare their properties to those found in both local and high-redshift star-forming galaxies. We find that in LIRGs, the star-forming clumps have radii ranging from $sim90-900$ pc and star formation rates (SFRs) of $sim1times10^{-3}$ to 10 M$_odot$yr$^{-1}$, with median values for extra-nuclear clumps of 170 pc and 0.03 M$_odot$yr$^{-1}$. The detected star-forming clumps are young, with a median stellar age of $8.7$ Myrs, and a median stellar mass of $5times10^{5}$ M$_odot$. The SFRs span the range of those found in normal local star-forming galaxies to those found in high-redshift star-forming galaxies at $rm{z}=1-3$. The luminosity function of the LIRG clumps has a flatter slope than found in lower-luminosity, star-forming galaxies, indicating a relative excess of luminous star-forming clumps. In order to predict the possible range of star-forming histories and gas fractions, we compare the star-forming clumps to those measured in the MassiveFIRE high-resolution cosmological simulation. The star-forming clumps in MassiveFIRE cover the same range of SFRs and sizes found in the local LIRGs and have total gas fractions that extend from 10 to 90%. If local LIRGs are similar to these simulated galaxies, we expect future observations with ALMA will find a large range of gas fractions, and corresponding star formation efficiencies, among the star-forming clumps in LIRGs.
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