Search

We present multiwavelength global star formation rate (SFR) estimates for 326 galaxies from the Star Formation Reference Survey in order to determine the mutual scatter and range of validity of different indicators. The widely used empirical SFR recipes based on 1.4 GHz continuum, 8.0  |$\mu$| m polycyclic aromatic hydrocarbons (PAHs), and a combination of far-infrared (FIR) plus ultraviolet (UV) emission are mutually consistent with scatter of |$\lesssim$| 0.3 dex. The scatter is even smaller, |$\lesssim$| 0.24 dex, in the intermediate luminosity range |$9.3\lt \log ({L_{60}\, \rm{\mu\,\,m}}/{\mbox{L$_\odot $}})\lt 10.7$|⁠. The data prefer a non-linear relation between 1.4 GHz luminosity and other SFR measures. PAH luminosity underestimates SFR for galaxies with strong UV emission. A bolometric extinction correction to far-UV luminosity yields SFR within 0.2 dex of the total SFR estimate, but extinction corrections based on UV spectral slope or nuclear Balmer decrement give SFRs that may differ from the total SFR by up to 2 dex. However, for the minority of galaxies with UV luminosity >5 × 109 L⊙ or with implied far-UV extinction <1 mag, the UV spectral slope gives extinction corrections with 0.22 dex uncertainty. [ABSTRACT FROM AUTHOR]

We report the results of a study exploring the stellar populations of 13 luminous (L > 1.2L*), spectroscopically confirmed, galaxies in the redshift interval 5.5 < z < 6.5, all with Hubble Space Telescope (HST) Wide Field Camera 3/infrared and Spitzer Infrared Array Camera imaging from the HST/Cosmic Assembly Near-infrared Deep Survey and Spitzer Extended Deep Survey. Based on fitting the observed photometry with galaxy spectral energy distribution (SED) templates covering a wide range of different star formation histories, including exponentially increasing star formation rates and a self-consistent treatment of Lyα emission, we find that the derived stellar masses lie within the range of 109< M* < 1010 M⊙ and are robust to within a factor of 2. In contrast, we confirm previous reports that the ages of the stellar populations are poorly constrained. Although the best-fitting models for 3/13 of the sample have ages of ≳300 Myr, the degeneracies introduced by dust extinction mean that only two of these objects actually require a ≳300 Myr old stellar population to reproduce the observed photometry. We also explore SED fitting with more general, two-component models (burst plus ongoing star formation), thereby relaxing the requirement that the current star formation rate and assembled stellar mass must be coupled, and allow for nebular line+continuum emission. On average, the inclusion of nebular emission leads to lower stellar mass estimates (median offset 0.18 dex), moderately higher specific star formation rates, and allows for a wider range of plausible stellar ages. However, based on our SED modelling, we find no strong evidence for extremely young ages in our sample (i.e. <50 Myr). Finally, considering all of the different star formation histories explored, we find that the median best-fitting ages are of the order of ≃200–300 Myr and that the objects with the tightest constraints indicate ages in the range of 50–200 Myr. [ABSTRACT FROM AUTHOR]

We present results of a large survey of the mid-infrared (mid-IR) properties of 248 Lyman Break Galaxies (LBGs) with confirmed spectroscopic redshift using deep Spitzer/Infrared Array Camera (IRAC) observations in six cosmological fields. By combining the new mid-IR photometry with optical and near-infrared observations, we model the spectral energy distributions (SEDs) employing a revised version of the Bruzual and Charlot synthesis population code that incorporates a new treatment of the thermal-pulsating asymptotic giant branch phase (CB07). Our primary aim is to investigate the impact of the AGB phase in the stellar masses of the LBGs, and compare our new results with previous stellar mass estimates. We investigate the stellar mass of the LBG population as a whole and assess the benefits of adding longer wavelengths to estimates of stellar masses for high-redshift galaxies. Based on the new CB07 code, we find that the stellar masses of LBGs are smaller on an average by a factor of ∼1.4 compared to previous estimates. LBGs with 8 and/or 24 μm detections show higher masses than LBGs faint in the IRAC bands . The ages of these massive LBGs are considerably higher than the rest of the population, indicating that they have been star forming for at least ∼1 Gyr. We also show how the addition of the IRAC bands improves the accuracy of the estimated stellar masses and reduced the scatter on the derived mass-to-light ratios. In particular, we present a tight correlation between the 8 μm IRAC band (rest-frame K for galaxies at ) and the stellar mass. We calculate the number density of massive LBGs and find it to be times lower than that found by previous studies. Finally, based on ultraviolet-corrected star formation rates (SFRs), we investigate the SFR–stellar mass correlation at , find it similar to the one observed at other redshifts and show that our data place the peak of the evolution of the specific SFR at . [ABSTRACT FROM AUTHOR]

We present millimetre observations of a sample of 12 high-redshift ultraluminous infrared galaxies (ULIRGs) in the extended growth strip (EGS). These objects were initially selected on the basis of their observed mid-IR colours ( and ) to lie at high redshift , and subsequent 20–38 μm mid-IR spectroscopy confirms that they lie in a narrow redshift window centred on . We detect 9/12 of the objects in our sample at high significance with a mean 1200 μm flux of mJy. Our millimetre photometry, combined with existing far-IR photometry from the Far-IR Deep Extragalactic Legacy Survey (FIDELS) and accurate spectroscopic redshifts, places constraints both sides of the thermal dust peak. This allows us to estimate the dust properties, including the far-IR luminosity, dust temperature and dust mass. We find that our sample is similar to other high- z and intermediate- z ULIRGs, and local systems, but has a different dust selection function than submillimeter-selected galaxies. Finally, we use existing 20-cm radio continuum imaging to test the far-IR/radio correlation at high redshift. We find that our sample is consistent with the local relation, implying little evolution. Furthermore, this suggests that our sample selection method is efficient at identifying ultraluminous, starburst-dominated systems within a very narrow redshift range centred at . [ABSTRACT FROM AUTHOR]