Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe bursting nature of star formation in compact star-forming galaxies from the Sloan Digital Sky Survey
427
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We study integrated characteristics of ~14000 low-redshift (0<z<1) compact star-forming galaxies (SFGs) selected from the Data Release 12 of the Sloan Digital Sky Survey. It is found that emission of these galaxies is dominated by strong young bursts of star formation, implying that their luminosities experience rapid variations on a time scale of a few Myr. Reducing integrated characteristics of these galaxies to zero burst age would result in a considerably tighter and almost linear relation between stellar mass and star formation rate (SFR). The same correction implies that the specific star formation rate (the ratio of SFR and stellar mass) is not dependent on the galaxy stellar mass. We conclude that the correction for rapid luminosity evolution must be taken into account in a similar way when comparing different samples of low- and high-redshift SFGs. If the bursting nature of star formation and young burst ages are characteristics of the galaxies selected at high redshifts, the age correction of observed SFRs derived from the Hbeta emission line or UV continua would modify the derived SFR densities in the early universe.
rate research
Read More
We study Red Misfits, a population of red, star-forming galaxies in the local Universe. We classify galaxies based on inclination-corrected optical colours and specific star formation rates derived from the Sloan Digital Sky Survey Data Release 7. Although the majority of blue galaxies are star-forming and most red galaxies exhibit little to no ongoing star formation, a small but significant population of galaxies ($sim$11 per cent at all stellar masses) are classified as red in colour yet actively star-forming. We explore a number of properties of these galaxies and demonstrate that Red Misfits are not simply dusty or highly-inclined blue cloud galaxies or quiescent red galaxies with poorly-constrained star formation. The proportion of Red Misfits is nearly independent of environment and this population exhibits both intermediate morphologies and an enhanced likelihood of hosting an AGN. We conclude that Red Misfits are a transition population, gradually quenching on their way to the red sequence and this quenching is dominated by internal processes rather than environmentally-driven processes. We discuss the connection between Red Misfits and other transition galaxy populations, namely S0s, red spirals and green valley galaxies.
We study the evolution of 82302 star-forming (SF) galaxies from the SDSS. Our main goals are to explore new ways of handling star formation histories (SFH) obtained with our publicly available spectral synthesis code STARLIGHT, and apply them to investigate how SFHs vary as a function of nebular metallicity (Zneb). Our main results are: (1) A conventional correlation analysis shows how global properties such as luminosity, mass, dust content, mean stellar metallicity and mean stellar age relate to Zneb. (2) We present a simple formalism which compresses the results of the synthesis into time-dependent star formation rates (SFR) and mass assembly histories. (3) The current SFR derived from the population synthesis and that from H-alpha are shown to agree within a factor of two. Thus we now have a way to estimate SFR in AGN hosts, where the H-alpha method cannot be applied. (4) Fully time-dependent SFHs are derived for all galaxies and averaged over six Zneb bins spanning the entire SF wing in the [OIII]/H-beta X [NII]/H-alpha diagram. (5) We find that SFHs vary systematically along the SF sequence, such that low-Zneb systems evolve slower and are currently forming stars at a higher relative rate. (6) At any given time, the distribution of specific SFRs for galaxies within a Zneb-bin is broad and roughly log-normal. (7) The same results are found grouping galaxies in stellar mass (M*) or surface mass density (S*) bins. (8) The overall pattern of SFHs as a function of Zneb, M* or S* is robust against changes in selection criteria, choice of evolutionary synthesis models for the spectral fits, and differential extinction effects. (Abridged)
(abridged) We studied a large sample of ~14000 dwarf star-forming galaxies with strong emission lines selected from the Sloan Digital Sky Survey (SDSS) and distributed in the redshift range of z~0-0.6. We modelled spectral energy distributions (SED) of all galaxies which were based on the SDSS spectra in the visible range of 0.38-0.92 micron and included both the stellar and ionised gas emission. These SEDs were extrapolated to the UV and mid-infrared ranges to cover the wavelength range of 0.1-22 micron. The SDSS spectroscopic data were supplemented by photometric data from the GALEX, SDSS, 2MASS, WISE, IRAS, and NVSS all-sky surveys. We derived global characteristics of the galaxies, such as their element abundances, luminosities, and stellar masses. The luminosities and stellar masses range within the sample over ~5 orders of magnitude, thereby linking low-mass and low-luminosity blue compact dwarf (BCD) galaxies to luminous galaxies, which are similar to high-redshift Lyman-break galaxies (LBGs). The luminosity L(Hbeta) of the Hbeta emission line, a characteristic of the youngest stellar population with an age of a few Myr, is correlated with luminosities in other wavelength ranges. This implies that the most recent burst of star formation makes a significant contribution to the emission in the visible range and dominates in other wavelength ranges. We found 20 galaxies with very red WISE mid-infrared m(3.4micron)-m(4.6micron) colour (>2 mag), which suggests the important contribution of the hot (with a temperature of several hundred degree) dust emission in these galaxies. Our analysis of the balance between the luminosity in the WISE bands that covered a wavelength range of 3.4-22 micron and the luminosity of the emission absorbed at shorter wavelengths showed that the luminosity of the hot dust emission is increased with increasing L(Hbeta) and EW(Hbeta).
An important question in extragalactic astronomy concerns the distribution of black hole accretion rates of active galactic nuclei (AGN). Based on observations at X-ray wavelengths, the observed Eddington ratio distribution appears as a power law, while optical studies have often yielded a lognormal distribution. There is increasing evidence that these observed discrepancies may be due to contamination by star formation and other selection effects. Using a sample of galaxies from the Sloan Digital Sky Survey Data Release 7, we test if an intrinsic Eddington ratio distribution that takes the form of a Schechter function is consistent with previous work that suggests that young galaxies in optical surveys have an observed lognormal Eddington ratio distribution. We simulate the optical emission line properties of a population of galaxies and AGN using a broad instantaneous luminosity distribution described by a Schechter function near the Eddington limit. This simulated AGN population is then compared to observed galaxies via the positions on an emission line excitation diagram and Eddington ratio distributions. We present an improved method for extracting the AGN distribution using BPT diagnostics that allows us to probe over one order of magnitude lower in Eddington ratio counteracting the effects of dilution by star formation. We conclude that for optically selected AGN in young galaxies, the intrinsic Eddington ratio distribution is consistent with a possibly universal, broad power law with an exponential cutoff, as this distribution is observed in old optically selected galaxies and in X-rays.
Galaxies are usually classified as star forming or active by using diagnostic diagrams, such as [N II]/Halpha vs. [O III]/Hbeta. Active galaxies are further classified into Seyfert or LINER-like sources. We claim that a non-negligible fraction of galaxies classified as LINERs in the Sloan Digital Sky Survey are in fact ionized by hot post-AGB stars and white dwarfs.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
