SPECTROSCOPIC OBSERVATIONS OF LYMAN BREAK GALAXIES AT REDSHIFTS ∼4, 5, AND 6 IN THE GOODS-SOUTH FIELD (original) (raw)
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Lyman break and UV-selected galaxies at z ∼ 1
2016
In this work we report the PACS-100µm/160µm detections of a sample of 42 GALEXselected and FIR-detected Lyman break galaxies (LBGs) at z ∼ 1 located in the COSMOS field and analyze their ultraviolet (UV) to far-infrared (FIR) properties. The detection of these LBGs in the FIR indicates that they have a dust content high enough so that its emission can be directly detected. According to a spectral energy distribution (SED) fitting with stellar population templates to their UV-to-near-IR observed photometry, PACS-detected LBGs tend to be bigger (R eff ∼ 4.1 kpc), more massive (log (M * /M ⊙) ∼ 10.7), dustier (E s (B − V) ∼ 0.40), redder in the UV continuum (β ∼ −0.60), and UV-brighter (log (L UV /L ⊙) ∼ 10.1) than PACS-undetected LBGs. PACS-detected LBGs at z ∼ 1 are mostly disk-like galaxies and are located over the green-valley and red sequence of the color-magnitude diagram of galaxies at their redshift. By using their UV and IR emission, we find that PACS-detected LBGs tend to be less dusty and have slightly higher total star-formation rates (SFRs) than other PACS-detected UV-selected galaxies within their same redshift range. As a consequence of the selection effect due to the depth of the FIR observations employed, all our PACS-detected LBGs have total IR luminosities, L IR , higher than 10 11 L ⊙ and thus are luminous IR galaxies (LIRGs). However, none of the PACS-detected LBGs are in the ultra-luminous IR galaxies (ULIRGs) regime, L IR 10 12 L ⊙ , where the FIR observations are complete. The finding of ULIRGs-LBGs at higher redshifts (z ∼ 3) suggests an evolution of the FIR emission of LBGs with cosmic time. In an IRX-β diagram, PACS-detected LBGs at z ∼ 1 tend to be located around the relation for local starburst similarly to other UV-selected PACS-detected galaxies at their same redshift. Consequently, the dust-correction factors obtained with their UV continuum slope allow to determine their total SFR, unlike at higher redshifts. However, the dust attenuation derived from UV to NIR SED fitting overestimates the total SFR for most of our PACS-detected LBGs in age-dependent way: the overestimation factor is higher in younger galaxies. This is likely due to the typical degeneracy between dust attenuation and age in the SED-fitting with synthetic templates and highlights the importance of the FIR measurements in the analysis of star-forming galaxies at intermediate redshifts.
The Astrophysical Journal, 2013
We present deep HST near-IR and Spitzer mid-IR observations of a large sample of spectroscopicallyconfirmed galaxies at z ≥ 6. The sample consists of 51 Lyα emitters (LAEs) at z ≃ 5.7, 6.5, and 7.0, and 16 Lyman-break galaxies (LBGs) at 5.9 ≤ z ≤ 6.5. The near-IR images were mostly obtained with WFC3 in the F125W and F160W bands, and the mid-IR images were obtained with IRAC in the 3.6µm and 4.5µm bands. Our galaxies also have deep optical imaging data from Subaru Suprime-Cam. We utilize the multi-band data and secure redshifts to derive their rest-frame UV properties. These galaxies have steep UV continuum slopes roughly between β ≃ −1.5 and -3.5, with an average value of β ≃ −2.3, slightly steeper than the slopes of LBGs in previous studies. The slope shows little dependence on UV continuum luminosity except for a few of the brightest galaxies. We find a statistically significant excess of galaxies with slopes around β ≃ −3, suggesting the existence of very young stellar populations with extremely low metallicity and dust content. Our galaxies have moderately strong rest-frame Lyα equivalent width (EW) in a range of ∼10 to ∼200Å. The starformation rates are also moderate, from a few to a few tens solar masses per year. The LAEs and LBGs in this sample share many common properties, implying that LAEs represent a subset of LBGs with strong Lyα emission. Finally, the comparison of the UV luminosity functions between LAEs and LBGs suggests that there exists a substantial population of faint galaxies with weak Lyα emission (EW < 20Å) that could be the dominant contribution to the total ionizing flux at z ≥ 6.
A Magellan IMACS Spectroscopic Search for Lyα‐emitting Galaxies at Redshift 5.7
The Astrophysical Journal, 2008
We present results from a blind, spectroscopic survey for z ∼ 5.7 Lyα -emitting galaxies using the Inamori Magellan Areal Camera and Spectrograph. A total of ∼ 200 square arcminutes were observed in the COSMOS and LCIRS fields using a narrowband filter, which transmits between atmospheric emission lines at 8190Å, and a mask with 100 longslits. This observing technique provides higher emissionline sensitivity than narrowband imaging and probes larger volumes than strong lensing. We find 170 emission-line galaxies and identify their redshifts spectroscopically. We confirm three Lyα emitting galaxies (LAEs), the first discovered using multislit-narrowband spectroscopy. Their line profiles are narrow, but fitted models suggest instrinsic, unattenuated widths ∼ 400 km s −1 FWHM. The red wing of the line profiles present features consistent with galactic winds. The star formation rates of these galaxies are at least 5-7 M ⊙ yr −1 and likely a factor of two higher. We estimate the number density of L ≥ 5 × 10 42 ergs s −1 LAEs is 9.0 +12 −4 × 10 −5 h 3 70 Mpc −3 at redshift 5.7 and constrain the Schechter function parameters describing this population. Galaxies fainter than our detection limit may well be the primary source of ionizing photons at z ∼ 6. We argue, however, that the break luminosity L * ,Lyα is not yet well constrained. If this break luminosity is near our detection limit, and somewhat lower than previous estimates, then the detected LAE population could be responsible for ionizing the intergalactic gas at redshift z ∼ 6. We discuss the potential of multislit-narrowband spectroscopy for deeper emissionline surveys.
SPECTROSCOPIC CONFIRMATION OF TWO LYMAN BREAK GALAXIES AT REDSHIFT BEYOND 7
The Astrophysical Journal, 2011
We report the spectroscopic confirmation of two Lyman break galaxies at redshift > 7. The galaxies were observed as part of an ultra-deep spectroscopic campaign with FORS2 at the ESO/VLT for the confirmation of z ≃ 7 "z-band dropout" candidates selected from our VLT/Hawk-I imaging survey. Both galaxies show a prominent emission line at 9735Å and 9858Å respectively: the lines have fluxes around ∼ 1 − 1.2 × 10 −17 ergs −1 cm −2 and exhibit a sharp decline on the blue side and a tail on the red side. The asymmetry is quantitatively comparable to the observed asymmetry in z ∼ 6 Lyα lines, where absorption by neutral hydrogen in the IGM truncates the blue side of the emission line profile. We carefully evaluate the possibility that the galaxies are instead at lower redshift and we are observing either [O ii], [O iii] or Hα emission: however from the spectroscopic and the photometric data we conclude that there are no other plausible identifications, except for Lyα at redshift >7, making these the first robust Lyman break galaxies ever confirmed at redshift beyond 7. Based on their redshifts and broad-band photometry, we derive limits on the star formation rate and on the ultraviolet spectral slopes of the two galaxies. We argue that these two galaxies alone are unlikely to have ionized the IGM in their surroundings.
A NEW CONSTRAINT ON THE LyαFRACTION OF UV VERY BRIGHT GALAXIES AT REDSHIFT 7
The Astrophysical Journal, 2016
We study the extent to which very bright (-< <-M 23.0 21.75 UV) Lyman-break-selected galaxies at redshifts z 7 display detectable Lyα emission. To explore this issue, we obtained follow-up optical spectroscopy of 9 z 7 galaxies from a parent sample of 24 z 7 galaxy candidates selected from the 1.65 deg 2 COSMOS-UltraVISTA and SXDS-UDS survey fields using the latest near-infrared public survey data, and new ultra-deep Subaru z′-band imaging (which we also present and describe in this paper). Our spectroscopy yielded only one possible detection of Lyα at z = 7.168 with a rest-frame equivalent width Å =-+ EW 3.7 0 1.1 1.7. The relative weakness of this line, combined with our failure to detect Lyα emission from the other spectroscopic targets, allows us to place a new upper limit on the prevalence of strong Lyα emission at these redshifts. For conservative calculation and to facilitate comparison with previous studies at lower redshifts, we derive a 1σ upper limit on the fraction of UV-bright galaxies at z 7 that display Å > EW 50 0 , which we estimate to be <0.23. This result may indicate a weak trend where the fraction of strong Lyα emitters ceases to rise, and possibly falls between z;6 and z 7. Our results also leave open the possibility that strong Lyα may still be more prevalent in the brightest galaxies in the reionization era than their fainter counterparts. A larger spectroscopic sample of galaxies is required to derive a more reliable constraint on the neutral hydrogen fraction atz 7 based on the Lyα fraction in the bright galaxies.
Astronomy & Astrophysics, 2012
Context. The study of the dust extinction in high-redshift galaxies is fundamental to obtain an estimate of the corrected Star Formation Rate Density (SFRD) and to put constraints on galaxy evolution models. Aims. We plan to analyse dust extinction in Lyman Break Galaxies (LBGs) by introducing a new and more reliable approach to their selection and to the characterization of their distribution of UV slopes β, using deep IR images from HST. We fully discuss the methodology and the results focusing on a robust sample of z∼4 LBGs. Methods. We exploit deep WFC3 IR observations of the ERS and HUDF fields over GOODS-South, combined with HST-ACS optical data, to select z∼4 LBGs through a new (B-V) vs. (V-H) colour diagram. The UV slope of the selected galaxies is robustly determined by a linear fit over their observed I, Z, Y, J magnitudes, coherently with the original definition of β. The same fit is used to determine their rest-frame UV magnitudes M 1600 through a simple interpolation. We estimate the effect of observational uncertainties with detailed simulations that we also exploit, under a parametric maximum-likelihood approach, to constrain the probability density function of UV slopes PDF(β) as a function of rest-frame magnitude. Results. We find 142 and 25 robust LBGs in the ERS and HUDF fields respectively, limiting our sample to S/N(H)>10 objects. Our newly defined criteria improve the selection of z ∼4 LBGs and allow us to exclude red interlopers at lower redshift, especially z∼3-3.5 objects. We show that the use of a linear fit to estimate β and an accurate characterization of observational effects are required in such analysis of flux limited samples. We find that z ∼4 LBGs are characterized by blue UV slopes, suggesting a low dust extinction: all L < L * galaxies have an average UV slope β ≃ −2.1, while brighter objects only are slightly redder ( β ≃ −1.9). We find an intrinsic dispersion ≃ 0.3 for PDF(β) at all magnitudes. The SFRD at z∼4 corrected according to these estimates turns out to be lower than previously found: log(SFRD)≃ −1.09 M ⊙ /yr/M pc 3 . Finally, we discuss how the UV slope of z∼4 galaxies changes as a function of the dust-corrected UV magnitude (i.e. SFR). We show that most galaxies with a high SFR ( 80 M ⊙ /yr) are highly extincted objects. Among galaxies with lower SFR, we detect many with a much lower amount of reddening, although current observational limits prevent us from detecting those with high extinction, if they exist.
Spectroscopy of z∼ 5 Lyman break galaxies in the ESO Remote Galaxy Survey
Monthly Notices of the Royal Astronomical Society, 2010
We present the global results of a large spectroscopic survey carried out in order to identify z ∼ 5 Lyman break galaxies (LBGs) across ten widely-separated ∼ 45 arcmin 2 fields to a depth of I AB = 26.3. The redshifts of seventy 4.6 < z < 5.6 LBGs were identified through their Lyα emission and/or a strong continuum break, with thirty eight sources showing detectable line emission of between 2.6×10 −18 and 7×10 −17 erg cm −2 s −1. Just over half of the spectroscopically-confirmed z ∼ 5 galaxies have rest-frame Lyα equivalent widths above 20Å, double the frequency of similarly strong line emitters in similar z ∼ 3 LBG samples. However, when reasonable corrections are made for the spectroscopically-unconfirmed sources that are nevertheless at these redshifts in both samples,we find no significant difference in the frequency of high equivalent-width line emitters between the samples. The rest-frame UV continuum slope of a typical z ∼ 5 line-emitting galaxy (as measured primarily from photometry, but also apparent in spectroscopy) is bluer than that of a typical break-only galaxy, a difference that is difficult to explain purely by differences in the ages of their stellar populations. Variation in metallicity and/or dust extinction can more straightforwardly account for this difference. If the correlation between metallicity and UV continuum slope identified at low redshift is applicable at z > 3, the typical z ∼ 5 LBGs have metallicities a factor of three lower than those of LBGs at z ∼ 3. HST imaging of a subset of the LBGs indicates that a large majority of the spectroscopically-confirmed LBGs in our sample are members of multiple systems (on ∼ arcsec scales) and/or show disturbed morphology. Using local LBG analogues as a model, this multiplicity could be explained either by super-starburst regions within a larger unseen structure, or by a high incidence of merging events at this epoch. The current data cannot distinguish between these two possibilities. The surface density of z ∼ 5 LBGs in two of the ten fields is considerably higher than in the rest. Both show clear spikes in their redshift distributions indicating strong three-dimensional clustering in these fields. Against an expectation of about one source per 0.1 in redshift between 4.8 < z < 5.6, one field has seven identified objects between 5.11 < z < 5.21 and the other has 17 between 4.95 < z < 5.15. Neither structure can be bound given their depth in redshift and probably extend beyond the observed fields. The three-dimensional distances between LBGs in the structures are too large for them to have triggered their starbursts through mutual gravitational interaction, and so it is likely that the short-lived LBGs represent only a small fraction of the baryons in the structures.
Lyman Break and ultraviolet-selected galaxies at z 1 - II. PACS 100 m/160 m FIR detections
Monthly Notices of the Royal Astronomical Society, 2013
In this work we report the PACS-100µm/160µm detections of a sample of 42 GALEXselected and FIR-detected Lyman break galaxies (LBGs) at z ∼ 1 located in the COSMOS field and analyze their ultraviolet (UV) to far-infrared (FIR) properties. The detection of these LBGs in the FIR indicates that they have a dust content high enough so that its emission can be directly detected. According to a spectral energy distribution (SED) fitting with stellar population templates to their UV-to-near-IR observed photometry, PACS-detected LBGs tend to be bigger (R eff ∼ 4.1 kpc), more massive (log (M * /M ⊙) ∼ 10.7), dustier (E s (B − V) ∼ 0.40), redder in the UV continuum (β ∼ −0.60), and UV-brighter (log (L UV /L ⊙) ∼ 10.1) than PACS-undetected LBGs. PACS-detected LBGs at z ∼ 1 are mostly disk-like galaxies and are located over the green-valley and red sequence of the color-magnitude diagram of galaxies at their redshift. By using their UV and IR emission, we find that PACS-detected LBGs tend to be less dusty and have slightly higher total star-formation rates (SFRs) than other PACS-detected UV-selected galaxies within their same redshift range. As a consequence of the selection effect due to the depth of the FIR observations employed, all our PACS-detected LBGs have total IR luminosities, L IR , higher than 10 11 L ⊙ and thus are luminous IR galaxies (LIRGs). However, none of the PACS-detected LBGs are in the ultra-luminous IR galaxies (ULIRGs) regime, L IR 10 12 L ⊙ , where the FIR observations are complete. The finding of ULIRGs-LBGs at higher redshifts (z ∼ 3) suggests an evolution of the FIR emission of LBGs with cosmic time. In an IRX-β diagram, PACS-detected LBGs at z ∼ 1 tend to be located around the relation for local starburst similarly to other UV-selected PACS-detected galaxies at their same redshift. Consequently, the dust-correction factors obtained with their UV continuum slope allow to determine their total SFR, unlike at higher redshifts. However, the dust attenuation derived from UV to NIR SED fitting overestimates the total SFR for most of our PACS-detected LBGs in age-dependent way: the overestimation factor is higher in younger galaxies. This is likely due to the typical degeneracy between dust attenuation and age in the SED-fitting with synthetic templates and highlights the importance of the FIR measurements in the analysis of star-forming galaxies at intermediate redshifts.
Spectroscopic Confirmation of a Substantial Population of Luminous Red Galaxies at Redshifts z>~2
Astrophysical Journal, 2003
We confirm spectroscopically the existence of a population of galaxies at z>~2 with rest-frame optical colors similar to normal nearby galaxies. The galaxies were identified by their red near-infrared colors in deep images obtained with ISAAC on the Very Large Telescope. Redshifts of six galaxies with Js-Ks>2.3 were measured from optical spectra obtained with the Keck Telescope. Five out of six are in the range 2.43<=z<=3.52, demonstrating that the Js-Ks color selection is quite efficient. The rest-frame ultraviolet spectra of confirmed z>2 galaxies display a range of properties, with two galaxies showing emission lines characteristic of AGN, two having Ly-alpha in emission, and one showing interstellar absorption lines only. Their full spectral energy distributions are well described by constant star formation models with ages 1.4-2.6 Gyr, except for one galaxy whose colors indicate a dusty starburst. The confirmed z>2 galaxies are very luminous, with Ks=19.2-19.9. Assuming that our bright spectroscopic sample is representative for the general population of Js-Ks selected objects, we find that the surface density of red z>~2 galaxies is ~0.9/arcmin^2 to Ks=21. The surface density is comparable to that of Lyman-break selected galaxies with Ks<21, when corrections are made for the different redshift distributions of the two samples. Although there will be some overlap between the two populations, most 'optical-break' galaxies are too faint in the rest-frame ultraviolet to be selected as Lyman-break galaxies. The most straightforward interpretation is that star formation in typical optical-break galaxies started earlier than in typical Lyman-break galaxies. Optical-break galaxies may be the oldest and most massive galaxies yet identified at z>2, and could evolve into early-type galaxies and bulges.