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Star formation rate in galaxies from UV, IR, and H-alpha estimators  [PDF]
Hiroyuki Hirashita,Veronique Buat,Akio K. Inoue
Physics , 2003, DOI: 10.1051/0004-6361:20031144
Abstract: Infrared (IR) luminosity of galaxies originating from dust emission can be used as an indicator of the star formation rate (SFR). Inoue et al. (2000, IHK) have derived a formula for the conversion from IR luminosity to SFR by using the following three quantities: the fraction of Lyman continuum luminosity absorbed by gas (f), the fraction of UV luminosity absorbed by dust (epsilon), and the fraction of dust heating from old (>10^8 yr) stellar populations (eta). We develop a method to estimate those three quantities based on the idea that the various way of SFR estimates should return the same SFR. After applying our method to samples of galaxies, the following results are obtained. First, our method is applied to star-forming galaxies, finding that f~0.6, epsilon~0.5, and eta~0.4 as representative values. Next, we apply the method to a starburst sample, which shows larger extinction than the star-forming galaxy sample. With the aid of f, epsilon, and eta, we estimate reliable SFRs. Moreover, the H-alpha luminosity, if the H-alpha extinction is corrected by using the Balmer decrement, is suitable for a statistical analysis of SFR, because the same correction factor for the Lyman continuum extinction is applicable to both normal and starburst galaxies over all the range of SFR. The metallicity dependence of f and epsilon is also tested: Only the latter proves to have a correlation with metallicity. As an extension of our result, we show that all UV, H-alpha, and IR comoving luminosity densities at z=0 give a consistent SFR (~ 3x10^{-2}h M_sun/Mpc^3). Useful formulae for SFR estimate are listed.
UV Continuum Slope and Dust Obscuration from z~6 to z~2: The Star Formation Rate Density at High Redshift  [PDF]
R. J. Bouwens,G. D. Illingworth,M. Franx,R-R. Chary,G. R. Meurer,C. J. Conselice,H. Ford,M. Giavalisco,P. van Dokkum
Physics , 2009, DOI: 10.1088/0004-637X/705/1/936
Abstract: We provide a systematic measurement of the rest-frame UV continuum slope beta over a wide range in redshift (z~2-6) and rest-frame UV luminosity (0.1-2L*) to improve estimates of the SFR density at high redshift. We utilize the deep optical and infrared data (ACS/NICMOS) over the CDF-S and HDF-N GOODS fields, as well as the UDF for our primary UBVi "dropout" sample. We correct the observed distributions for selection biases and photometric scatter. We find that the UV-continuum slope of the most luminous galaxies is substantially redder at z~2-4 than it is at z~5-6. Lower luminosity galaxies are also found to be bluer than higher luminosity galaxies at z~2.5 and z~4. We do not find a large number of galaxies with beta's as red as -1 in our dropout selections at z~4, and particularly at z>~5, even though such sources could be readily selected from our data. This suggests that star-forming galaxies at z>~5 almost universally have very blue UV-continuum slopes, and that there are not likely to be a substantial number of dust-obscured galaxies at z>~5 that are missed in "dropout" searches. Using the same relation between UV-continuum slope and dust extinction as found to be appropriate at z~0 and z~2, we estimate the average dust extinction of galaxies as a function of redshift and UV luminosity in a consistent way. We find that the estimated dust extinction increases substantially with cosmic time for the most UV luminous galaxies, but remains small (<~2x) at all times for lower luminosity galaxies. Because these same lower luminosity galaxies dominate the luminosity density in the UV, the overall dust extinction correction remains modest at all redshifts. We include the contribution from ULIRGs in our SFR density estimates at z~2-6, but find that they contribute only ~20% of the total at z~2.5 and <~10% at z>~4.
The Stellar Population and Star Formation Rates of z~1.5-1.6 [O II] Emitting Galaxies Selected from Narrow-Band Emission-Line Surveys  [PDF]
Chun Ly,Matthew A. Malkan,Nobunari Kashikawa,Masao Hayashi,Tohru Nagao,Kazuhiro Shimasaku,Kazuaki Ota,Nathaniel R. Ross
Physics , 2012, DOI: 10.1088/0004-637X/757/1/63
Abstract: 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 13\AA. 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 45\AA, 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 0.89\pm0.22. 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.
The unbiased measurement of UV spectral slopes in low luminosity galaxies at z=7  [PDF]
A. B. Rogers,R. J. McLure,J. S. Dunlop
Physics , 2012, DOI: 10.1093/mnras/sts515
Abstract: The Ultraviolet (UV) continuum slope beta, typically observed at z=7 in Hubble Space Telescope (HST) WFC3/IR bands via the J-H colour, is a useful indicator of the age, metallicity, and dust content of high-redshift stellar populations. Recent studies have shown that the redward evolution of beta with cosmic time from redshift 7 to 4 can be largely explained by a build up of dust. However, initial claims that faint z=7 galaxies in the Hubble Ultra Deep Field WFC3/IR imaging (HUDF09) were blue enough to require stellar populations of zero reddening, low metallicity and young ages, hitherto unseen in star-forming galaxies, have since been refuted and revised. Here we revisit the question of how best to measure the UV slope of z=7 galaxies through source recovery simulations, within the context of present and future ultra-deep imaging from HST. We consider how source detection, selection and colour measurement have each biased the measurement of beta in previous studies. After finding a robust method for measuring beta in the simulations (via a power law fit to all the available photometry), we remeasure the UV slopes of a sample of previously published low luminosity z=7 galaxy candidates. The mean UV slope of faint galaxies in this sample appears consistent with an intrinsic distribution of normal star-forming galaxies with beta=-2, although properly decoding the underlying distribution will require further imaging from the ongoing HUDF12 programme. We therefore go on to consider strategies for obtaining better constraints on the underlying distribution of UV slopes at z=7 from these new data, which will benefit particularly from the addition of imaging in a second J-band filter: F140W. We find that a precise and unbiased measurement of beta should then be possible.
Predictions for the intrinsic UV continuum properties of star forming galaxies and the implications for inferring dust extinction  [PDF]
Stephen M. Wilkins,Violeta Gonzalez-Perez,Cedric G. Lacey,Carlton M. Baugh
Physics , 2012, DOI: 10.1111/j.1365-2966.2012.21344.x
Abstract: The observed ultraviolet continuum (UVC) slope is potentially a powerful diagnostic of dust obscuration in star forming galaxies. However, the intrinsic slope is also sensitive to the form of the stellar initial mass function (IMF) and to the recent star formation and metal enrichment histories of a galaxy. Using the galform semi-analytical model of galaxy formation, we investigate the intrinsic distribution of UVC slopes. For star-forming galaxies, we find that the intrinsic distribution of UVC slopes at z=0, parameterised by the power law index beta, has a standard deviation of sigma_beta=0.30. This suggests an uncertainty on the inferred UV attenuation of A_fuv=0.7$ (assuming a Calzetti attenuation curve) for an individual object, even with perfect photometry. Furthermore, we find that the intrinsic UVC slope correlates with star formation rate, intrinsic UV luminosity, stellar mass and redshift. These correlations have implications for the interpretation of trends in the observed UVC slope with these quantities irrespective of the sample size or quality of the photometry. Our results suggest that in some cases the attenuation by dust has been incorrectly estimated.
On the influence of physical galaxy properties on Lyman-alpha escape in star-forming galaxies  [PDF]
Hakim Atek,Daniel Kunth,Daniel Schaerer,J. Miguel Mas-Hesse,Matthew Hayes,Goran Ostlin,Jean-Paul Kneib,.
Physics , 2013, DOI: 10.1051/0004-6361/201321519
Abstract: [abridged] Among the different observational techniques used to select high-redshift galaxies, the hydrogen recombination line Lyman-alpha (Lya) is of particular interest as it gives access to the measurement of cosmological quantities such as the star formation rate of distant galaxy populations. However, the interpretation of this line and the calibration of such observables is still subject to serious uncertainties. Therefore, it important to understand under what conditions the Lya line can be used as a reliable star formation diagnostic tool. We use a sample of 24 Lya emitters at z ~ 0.3 with an optical spectroscopic follow-up to calculate the Lya escape fraction and its dependency upon different physical properties. We also examine the reliability of Lya as a star formation rate indicator. We combine these observations with a compilation of Lya emitters selected at z = 0 - 0.3 to assemble a larger sample. The Lya escape fraction depends clearly on the dust extinction following the relation fesc(Lya) = C(Lya) x 10^(-0.4 E(B-V) k(Lya)), but with a shallower slope than previously reported, with k(Lya) ~ 6.67 and C(Lya) = 0.22. However, the correlation does not follow the expected curve for a simple dust attenuation. We explore the various mechanisms than lead to fesc(Lya) values above the continuum extinction curve, i.e. to an enhancement of the Lya output. We also observe that the strength of Lya and the escape fraction appear unrelated to the galaxy metallicity. Regarding the reliability of Lya as a star formation rate (SFR) indicator, we show that the deviation of SFR(Lya) from the true SFR (as traced by the UV continuum) is a function of the observed SFR(UV), which can be seen as the decrease of fesc(Lya) with increasing UV luminosity. Moreover, we observe a redshift-dependence of this relationship revealing the underlying evolution of fesc(Lya) with redshift.
Interpreting the observed UV continuum slopes of high-redshift galaxies  [PDF]
Stephen M. Wilkins,Andrew Bunker,William Coulton,Rupert Croft,Tiziana Di Matteo,Nishikanta Khandai,Yu Feng
Physics , 2013, DOI: 10.1093/mnras/stt096
Abstract: The observed UV continuum slope of star forming galaxies is strongly affected by the presence of dust. Its observation is then a potentially valuable diagnostic of dust attenuation, particularly at high-redshift where other diagnostics are currently inaccesible. Interpreting the observed UV continuum slope in the context of dust attenuation is often achieved assuming the empirically calibrated Meurer et al. (1999) relation. Implicit in this relation is the assumption of an intrinsic UV continuum slope ($\beta=-2.23$). However, results from numerical simulations suggest that the intrinsic UV continuum slopes of high-redshift star forming galaxies are bluer than this, and moreover vary with redshift. Using values of the intrinsic slope predicted by numerical models of galaxy formation combined with a Calzetti et al. (2000) reddening law we infer UV attenuations ($A_{1500}$) $0.35-0.5\,{\rm mag}$ ($A_{V}$: $0.14-0.2\,{\rm mag}$ assuming Calzetti et al. 2000) greater than simply assuming the Meurer relation. This has significant implications for the inferred amount of dust attenuation at very-high ($z\approx 7$) redshift given current observational constraints on $\beta$, combined with the Meurer relation, suggest dust attenuation to be virtually zero in all but the most luminous systems.
UV-continuum slopes at z~4-7 from the HUDF09+ERS+CANDELS observations: Discovery of a well-defined UV-color magnitude relationship for z>=4 star-forming galaxies  [PDF]
R. J. Bouwens,G. D. Illingworth,P. A. Oesch,M. Franx,I. Labbe,M. Trenti,P. van Dokkum,C. M. Carollo,V. Gonzalez,R. Smit,D. Magee
Physics , 2011, DOI: 10.1088/0004-637X/754/2/83
Abstract: Ultra-deep ACS and WFC3/IR HUDF+HUDF09 data, along with the wide-area GOODS+ERS+CANDELS data over the CDF-S GOODS field, are used to measure UV colors, expressed as the UV-continuum slope beta, of star-forming galaxies over a wide range in luminosity (0.1L*(z=3) to 2L*(z=3)) at high redshift (z~7 to z~4). Beta is measured using all ACS and WFC3/IR passbands uncontaminated by Ly_alpha and spectral breaks. Extensive tests show that our beta measurements are only subject to minimal biases. Using a different selection procedure, Dunlop et al. recently found large biases in their beta measurements. To reconcile these different results, we simulated both approaches and found that beta measurements for faint sources are subject to large biases if the same passbands are used both to select the sources and to measure beta. High-redshift galaxies show a well-defined rest-frame UV color-magnitude (CM) relationship that becomes systematically bluer towards fainter UV luminosities. No evolution is seen in the slope of the UV CM relationship in the first 1.5 Gyr, though there is a small evolution in the zero-point to redder colors from z~7 to z~4. This suggests that galaxies are evolving along a well-defined sequence in the L(UV)-color (beta) plane (a "star-forming sequence"?). Dust appears to be the principal factor driving changes in the UV color (beta) with luminosity. These new larger beta samples lead to improved dust extinction estimates at z~4-7 and confirm that the extinction is still essentially zero at low luminosities and high redshifts. Inclusion of the new dust extinction results leads to (i) excellent agreement between the SFR density at z~4-8 and that inferred from the stellar mass density, and (ii) to higher SSFRs at z>~4, suggesting the SSFR may evolve modestly (by factors of ~2) from z~4-7 to z~2.
The UV Continuum of z > 1 Star-forming Galaxies in the Hubble Ultraviolet UltraDeep Field  [PDF]
Peter Kurczynski,Eric Gawiser,Marc Rafelski,Harry I. Teplitz,Viviana Acquaviva,Thomas M. Brown,Dan Coe,Duilia F. de Mello,Steven L. Finkelstein,Norman A. Grogin,Anton M. Koekemoer,Kyoung-soo Lee,Claudia Scarlata,Brian D. Siana
Physics , 2014, DOI: 10.1088/2041-8205/793/1/L5
Abstract: We estimate the UV continuum slope, beta, for 923 galaxies in the range 1 < z < 8 in the Hubble Ultradeep Field (HUDF). These data include 460 galaxies at 1 < z < 2 down to an absolute magnitude M_{UV} = -14 (~0.006 L*_{z=1}; 0.02 L*_{z=0}), comparable to dwarf galaxies in the local universe. We combine deep HST/UVIS photometry in F225W, F275W, F336W wavebands (UVUDF) with recent data from HST/WFC3/IR (HUDF12). Galaxies in the range 1 < z < 2 are significantly bluer than local dwarf galaxies. We find their mean (median) values = -1.382 (-1.830) +/- 0.002 (random) +/- 0.1 (systematic). We find comparable scatter in beta (standard deviation = 0.43) to local dwarf galaxies and 30% larger scatter than z > 2 galaxies. We study the trends of beta with redshift and absolute magnitude for binned sub-samples and find a modest color-magnitude relation, dbeta/dM = -0.11 +/- 0.01 and no evolution in dbeta/dM with redshift. A modest increase in dust reddening with redshift and luminosity, Delta E(B-V) ~ 0.1, and a comparable increase in the dispersion of dust reddening at z < 2, appears likely to explain the observed trends. At z > 2, we find trends that are consistent with previous works; combining our data with the literature in the range 1 < z < 8, we find a color evolution with redshift, dbeta/dz = -0.09 +/-0.01 for low luminosity (0.05 L*_{z=3}), and dbeta/dz = -0.06 +/-0.01 for medium luminosity (0.25 L*_{z=3}) galaxies.
The UV to FIR spectral energy distribution of star-forming galaxies in the redshift desert  [PDF]
I. Oteo,á. Bongiovanni,G. Magdis,A. M. Pérez-García,J. Cepa,H. Domínguez Sánchez,A. Ederoclite,M. Sánchez-Portal,I. Pintos-Castro
Physics , 2013, DOI: 10.1093/mnras/stt2468
Abstract: We analyse the rest-frame UV-to-NIR spectral energy distribution (SED) of Lyman break galaxies (LBGs), star-forming (SF) BzK (sBzK), and UV-selected galaxies at 1.5 < z < 2.5 in the COSMOS, GOODS-N, and GOODS-S fields. Additionally, we complement the multi-wavelength coverage of the galaxies located in the GOODS fields with deep FIR data taken from the GOODS-Herschel project. We find that sBzK galaxies represent the general population of SF galaxies at z ~ 2 better than LBGs. For a given stellar mass, LBGs tend to have bluer optical colours than sBzK and UV-selected galaxies. We find clean PACS individual detections for a subsample of 48 LBGs, 89 sBzK, and 91 UV-selected galaxies, that measure their dust emission directly. Their SFR_total = SFR_UV + SFR_IR cannot be recovered with the dust-correction factors derived with their continuum slope and the IRX-beta relations for local starbursts. This has implications, for example, in the definition of the main sequence (MS) at z ~ 2. PACS-detected galaxies are located above the z ~ 2 MS and thus their star formation is probably driven by starburst. This is in agreement with the shape of their IR SEDs. PACS-detected galaxies with redder UV continuum slope and higher stellar mass are more attenuated. We find that for a given UV continuum slope the dustiest galaxies at higher redshifts are more attenuated and that for a given stellar mass the dustiest galaxies at higher redshifts have stronger FIR emission. This suggests an evolution of their dust properties. However, we do not find significant evolution in the relation between dust attenuation and stellar mass with redshift, at least at z < 2.5. There is a subpopulation of 17, 26, and 27 LBGs, sBzK, and UV-selected galaxies, respectively, that are detected in any of the SPIRE bands. We speculate that SPIRE-detected LBGs are the bridging population between sub-mm galaxies and LBGs.
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