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Register a new userNew Constraints on the Star Formation Histories and Dust Attenuation of Galaxies in the Local Universe from GALEX
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We derive a variety of physical parameters including star formation rates (SFRs), dust attenuation and burst mass fractions for 6472 galaxies observed by the Galaxy Evolution Explorer (GALEX) and present in the SDSS DR1 main spectroscopic sample. Parameters are estimated in a statistical way by comparing each observed broad-band SED (two GALEX and five SDSS bands) with an extensive library of model galaxy SEDs, which cover a wide range of star formation histories and include stochastic starbursts. We compare the constraints derived using SDSS bands only with those derived using the combination of SDSS and GALEX photometry. We find that the addition of the GALEX bands leads to significant improvement in the estimation of both the dust optical depth and the star formation rate over timescales of 100 Myr to 1 Gyr in a galaxy. We are sensitive to SFRs as low as 10^{-3} M_sun/yr, and we find that low levels of star formation (SF) are mostly associated with early-type, red galaxies. The least massive galaxies have ratios of current to past-averaged SF rates (b-parameter) consistent with constant SF over a Hubble time. For late-type galaxies, this ratio on average decreases with mass. We find that b correlates tightly with NUV-r color, implying that the SF history of a galaxy can be constrained on the basis of the NUV-r color alone. The fraction of galaxies that have undergone a significant starburst episode within the last 1 Gyr steeply declines with mass-from ~20% for galaxies with ~10^8 M_sun to ~5% for ~10^11 M_sun galaxies.
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The majority of galaxies with current star-formation rates (SFRs), SFRo >= 10^-3 Msun/yr, in the Local Cosmological Volume where observations should be reliable, have the property that their observed SFRo is larger than their average star formation rate. This is in tension with the evolution of galaxies described by delayed-tau models, according to which the opposite would be expected. The tension is apparent in that local galaxies imply the star formation timescale tau approx 6.7 Gyr, much longer than the 3.5-4.5 Gyr obtained using an empirically determined main sequence at several redshifts. Using models where the SFR is a power law in time of the form propto (t - t1)^eta for t1 = 1.8 Gyr (with no stars forming prior to t1) implies that eta = 0.18 +- 0.03. This suggested near-constancy of a galaxys SFR over time raises non-trivial problems for the evolution and formation time of galaxies, but is broadly consistent with the observed decreasing main sequence with increasing age of the Universe.
We investigate the star formation histories (SFHs) of massive red spiral galaxies with stellar mass $M_ast>10^{10.5}M_odot$, and make comparisons with blue spirals and red ellipticals of similar masses. We make use of the integral field spectroscopy from the SDSS-IV/DR15 MaNGA sample, and estimate spatially resolved SFHs and stellar population properties of each galaxy by applying a Bayesian spectral fitting code to the MaNGA spectra. We find that both red spirals and red ellipticals have experienced only one major star formation episode at early times, and the result is independent of the adopted SFH model. On average, more than half of their stellar masses were formed $>$10 Gyrs ago, and more than 90% were formed $>6$ Gyrs ago. The two types of galaxies show similarly flat profiles in a variety of stellar population parameters: old stellar ages indicated by $D4000$ (the spectral break at around 4000AA), high stellar metallicities, large Mgb/Fe ratios indicating fast formation, and little stellar dust attenuation. In contrast, although blue spirals also formed their central regions $>$10 Gyrs ago, both their central regions and outer disks continuously form stars over a long timescale. Our results imply that, massive red spirals are likely to share some common processes of formation (and possibly quenching) with massive red ellipticals in the sense that both types were formed at $z > 2$ through a fast formation process.Possible mechanisms for the formation and quenching of massive red spirals are discussed.
We analyze a volume-limited sample of massive bulge-dominated galaxies with data from both the Sloan Digital Sky Survey and the Galaxy Evolution Explorer (GALEX) satellite. The galaxies have central velocity dispersions greater than 100 km/s and stellar surface mass densities that lie above the value where galaxies transition from actively star forming to passive systems. The sample is limited to redshifts 0.03<z<0.07. At these distances, the SDSS spectra sample the light from the bulge-dominated central regions of the galaxies. The GALEX NUV data provide high sensitivity to low rates of global star formation in these systems. Our sample of bulge-dominated galaxies exhibits a much larger dispersion in NUV-r colour than in optical g-r colour. Nearly all of the galaxies with bluer NUV-r colours are AGN. Both GALEX images and SDSS colour profiles demonstrate that the excess UV light is associated with an extended disk. We find that galaxies with red outer regions almost never have a young bulge or a strong AGN. Galaxies with blue outer regions have bulges and black holes that span a wide range in age and accretion rate. Galaxies with young bulges and strongly accreting black holes almost always have blue outer disks. Our suggested scenario is one in which the source of gas that builds the bulge and black hole is a low mass reservoir of cold gas in the disk.The presence of this gas is a necessary, but not sufficient condition for bulge and black hole growth. Some mechanism must transport this gas inwards in a time variable way. As the gas in the disk is converted into stars, the galaxies will turn red, but further gas infall can bring them back into the blue NUV-r sequence.(Abridged)
SPICA is one of the key projects for the future. Not only its instrument suite will open up a discovery window but they will also allow to physically understand some of the phenomena that we still do not understand in the high-redshift universe. Using new homogeneous luminosity functions (LFs) in the Far-Ultraviolet (FUV) from VVDS and in the Far-Infrared (FIR) from Herschel/PEP and Herschel/HerMES, we studied the evolution of the dust attenuation with redshift. With this information, we are able to estimate the redshift evolution of the total (FUV + FIR) star formation rate density (SFRD_TOT). Our main conclusions are that: 1) the dust attenuation A_FUV is found to increase from z = 0 to $z sim 1.2 and then starts to decrease until our last data point at z = 3.6; 2) the estimated SFRD confirms published results to z sim 2. At z > 2, we observe either a plateau or a small increase up to z sim 3 and then a likely decrease up to z = 3.6; 3) the peak of A_FUV is delayed with respect to the plateau of SFRD_TOT but the origin of this delay is not understood yet, and SPICA instruments will provide clues to move further in the physical understanding of this delay but also on the detection and redshift measurements of galaxies at higher redshifts. This work is further detailed in Burgarella et al. (2013).
We develop and implement an inclination-dependent attenuation prescription for spectral energy distribution (SED) fitting and study its impact on derived star-formation histories. We apply our prescription within the SED fitting code Lightning to a clean sample of 82, z = 0.21-1.35 disk-dominated galaxies in the Great Observatories Origins Deep Survey (GOODS) North and South fields. To compare our inclination-dependent attenuation prescription with more traditional fitting prescriptions, we also fit the SEDs with the inclination-independent Calzetti et al. (2000) attenuation curve. From this comparison, we find that fits to a subset of 58, z < 0.7 galaxies in our sample, utilizing the Calzetti et al. (2000) prescription, recover similar trends with inclination as the inclination-dependent fits for the FUV-band attenuation and recent star-formation rates. However, we find a difference between prescriptions in the optical attenuation (AV) that is strongly correlated with inclination (p-value < 10^-10). For more face-on galaxies, with i < 50 deg, (edge-on, i = 90 deg), the average derived AV is 0.30 +/- 0.10 magnitudes lower (0.55 +/- 0.15 magnitudes higher) for the inclination-dependent model compared to traditional methods. Further, the ratio of stellar masses between prescriptions also has a significant (p-value < 10^-2) trend with inclination. For i = 0-65 deg, stellar masses are systematically consistent between fits, with log(Mstar_inc/Mstar_Calzetti) = -0.05 +/- 0.03 dex, and scatter of 0.11 dex. However, for i = 80-90 deg, derived stellar masses are lower for the Calzetti et al. (2000) fits by an average factor of 0.17 +/- 0.02 dex, and scatter of 0.13 dex. Therefore, these results suggest that SED fitting assuming the Calzetti et al. (2000) attenuation law potentially underestimates stellar masses in highly inclined disk-dominated galaxies.
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