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Register a new userStar Formation in Emission-Line Galaxies Between Redshifts of 0.8 and 1.6
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Erin K.S. Hicks
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Optical spectra of 14 emission-line galaxies representative of the 1999 NICMOS parallel grism Ha survey of McCarthy et al. are presented. Of the 14, 9 have emission lines confirming the redshifts found in the grism survey. The higher resolution of our optical spectra improves the redshift accuracy by a factor of 5. The [O II]/Ha values of our sample are found to be more than two times lower than expected from Jansen et al. This [O II]/Ha ratio discrepancy is most likely explained by additional reddening in our Ha-selected sample [on average, as much as an extra E(B-V) = 0.6], as well as to a possible stronger dependence of the [O II]/Ha ratio on galaxy luminosity than is found in local galaxies. The result is that star formation rates (SFRs) calculated from [O II]3727 emission, uncorrected for extinction, are found to be on average 4 +/- 2 times lower than the SFRs calculated from Ha emission. Classification of emission-line galaxies as starburst or Seyfert galaxies based on comparison of the ratios [O II]/Hb and [Ne III]3869/Hb is discussed. New Seyfert 1 diagnostics using the Ha line luminosity, H-band absolute magnitude, and Ha equivalent widths are also presented. One galaxy is classified as a Seyfert 1 based on its broad emission lines, implying a comoving number density for Seyfert 1s of 2.5{+5.9, -2.1} times 10^{-5} Mpc^{-3}. This commoving number density is a factor of 2.4{+5.5,-2.0} times higher than estimated by other surveys.
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We perform SED fitting analysis on a COSMOS sample covering UV-to-FIR wavelengths with emission lines from the FMOS survey. The sample of 182 objects with H$alpha$ and [OIII]$lambda5007$ emission spans over a range of $1.40<rm{z}<1.68$. We obtain robust estimates of stellar mass ($10^{9.5}-10^{11.5}~rm{M_odot}$) and SFR ($10^1-10^3~rm{M_odot}~rm{yr}^{-1}$) from the Bayesian analysis with CIGALE fitting continuum photometry and H$alpha$. We obtain a median attenuation of A$_rm{Halpha}=1.16pm0.19$ mag and A$_rm{[OIII]}=1.41pm0.22$ mag. H$alpha$ and [OIII]$lambda5007$ attenuations are found to increase with stellar mass, confirming previous findings. A difference of $57$% in the attenuation experienced by emission lines and continuum is found in agreement with the lines being more attenuated than the continuum. New CLOUDY HII-region models in CIGALE enable good fits of H$alpha$, H$beta$, [OIII]$lambda5007$ emission lines with differences smaller than $0.2$ dex. Fitting [NII]$lambda6584$ line is challenging due to well-known discrepancies in the locus of galaxies in the BPT diagram at intermediate redshifts. We find a positive correlation for SFR and dust-corrected L$_rm{[OIII]lambda5007}$ and we derive the linear relation $log_{10}rm{(SFR/rm{M}_odot~rm{yr}^{-1})}=log_{10} (rm{L}_{[rm{OIII]}}/rm{ergs~s^{-1}})-(41.20pm0.02)$. Leaving the slope as a free parameter leads to $log_{10}rm{(SFR/rm{M}_odot~rm{yr}^{-1})}=(0.83pm0.06)log_{10}(rm{L}_{[rm{OIII]}}/rm{ergs~s^{-1}})-(34.01pm2.63)$. Gas-phase metallicity and ionization parameter variations account for a $0.24$ dex and $1.1$ dex of the dispersion, respectively. An average value of $logrm{U}approx-2.85$ is measured for this sample. Including HII-region models to fit simultaneously photometry and emission line fluxes are paramount to analyze future data from surveys such as MOONS and PFS.
We present the first detailed study of the stellar populations of star-forming galaxies at z~1.5, which are selected by their [O II] emission line, detected in narrow-band surveys. We identified ~1,300 [O II] emitters at z=1.47 and z=1.62 in the Subaru Deep Field with rest-frame EWs above 13AA. Optical and near-infrared spectroscopic observations for ~10% of our samples show that our separation of [O II] from [O III] emission-line galaxies in two-color space is 99% successful. We analyze the multi-wavelength properties of a subset of ~1,200 galaxies with the best photometry. They have average rest-frame EW of 45AA, stellar mass of 3 x 10^9 M_sun, and stellar age of 100 Myr. In addition, our SED fitting and broad-band colors indicate that [O II] emitters span the full range of galaxy populations at z~1.5. We also find that 80% of [O II] emitters are also photometrically classified as BX/BM (UV) galaxies and/or the star-forming BzK (near-IR) galaxies. Our [O II] emission line survey produces a far more complete, and somewhat deeper sample of z~1.5 galaxies than either the BX/BM or sBzK selection alone. We constructed average SEDs and find that higher [O II] EW galaxies have somewhat bluer continua. SED model-fitting shows that they have on average half the stellar mass of galaxies with lower [O II] EW. The observed [O II] luminosity is well-correlated with the far-UV continuum with a logarithmic slope slightly 0f 0.89pm0.22. The scatter of the [O II] luminosity against the far-UV continuum suggests that [O II] can be used as a SFR indicator with a reliability of 0.23 dex.
Twenty years ago, GRB 980425/SN 1998bw revealed that long Gamma-Ray Bursts (GRBs) are physically associated with broad-lined type Ic supernovae. Since then more than 1000 long GRBs have been localized to high angular precision, but only in about 50 cases the underlying supernova (SN) component was identified. Using the multi-channel imager GROND (Gamma-Ray Burst Optical Near-Infrared Detector) at ESO/La Silla, during the last ten years we have devoted a substantial amount of observing time to reveal and to study SN components in long-GRB afterglows. Here we report on four more GRB-SNe (associated with GRBs 071112C, 111228A, 120714B, and 130831A) which were discovered and/or followed-up with GROND and whose redshifts lie between z=0.4 and 0.8. We study their afterglow light curves, follow the associated SN bumps over several weeks, and characterize their host galaxies. Using SN 1998bw as a template, the derived SN explosion parameters are fully consistent with the corresponding properties of the so-far known GRB-SN ensemble, with no evidence for an evolution of their properties as a function of redshift. In two cases (GRB 120714B/SN 2012eb at z=0.398 and GRB 130831A/SN 2013fu at z=0.479) additional Very Large Telescope (VLT) spectroscopy of the associated SNe revealed a photospheric expansion velocity at maximum light of about 40 000 and 20 000 km/s, respectively. For GRB 120714B, which was an intermediate-luminosity burst, we find additional evidence for a blackbody component in the light of the optical transient at early times, similar to what has been detected in some GRB-SNe at lower redshifts.
We examine the evolutionary status of luminous, star-forming galaxies in intermediate-redshift clusters by considering their star formation rates and the chemical and ionsiation properties of their interstellar emitting gas. Our sample consists of 17 massive, star-forming, mostly disk galaxies with M_{B}<-20, in clusters with redshifts in the range 0.31< z <0.59, with a median of <z>=0.42. We compare these galaxies with the identically selected and analysed intermediate-redshift field sample of Mouhcine et al. (2006), and with local galaxies from the Nearby Field Galaxy Survey of Jansen et al. (2000). From our optical spectra we measure the equivalent widths of OII, Hbeta and OIII emission lines to determine diagnostic line ratios, oxygen abundances, and extinction-corrected star formation rates. The star-forming galaxies in intermediate-redshift clusters display emission line equivalent widths which are, on average, significantly smaller than measured for field galaxies at comparable redshifts. However, a contrasting fraction of our cluster galaxies have equivalent widths similar to the highest observed in the field. This tentatively suggests a bimodality in the star-formation rates per unit luminosity for galaxies in distant clusters. We find no evidence for further bimodalities, or differences between our cluster and field samples, when examining additional diagnostics and the oxygen abundances of our galaxies. This maybe because no such differences exist, perhaps because the cluster galaxies which still display signs of star-formation have recently arrived from the field. In order to examine this topic with more certainty, and to further investigate the way in which any disparity varies as a function of cluster properties, larger spectroscopic samples are needed.
We present the luminosity function of [OII]-emitting galaxies at a median redshift of z=0.9, as measured in the deep spectroscopic data in the STIS Parallel Survey (SPS). The luminosity function shows strong evolution from the local value, as expected. By using random lines of sight, the SPS measurement complements previous deep single field studies. We calculate the density of inferred star formation at this redshift by converting from [OII] to H-alpha line flux as a function of absolute magnitude and find rho_dot=0.043 +/- 0.014 Msun/yr/Mpc^3 at a median redshift z~0.9 within the range 0.46<z<1.415 (H_0 = 70 km/s/Mpc, Omega_M=0.3, Omega_Lambda=0.7. This density is consistent with a (1+z)^4 evolution in global star formation since z~1. To reconcile the density with similar measurements made by surveys targeting H-alpha may require substantial extinction correction.
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