HerMES: LYMAN BREAK GALAXIES INDIVIDUALLY DETECTED AT 0.7 ⩽ z ⩽ 2.0 IN GOODS-N WITH HERSCHEL /SPIRE (original) (raw)
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HerMES: Herschel-SPIRE observations of Lyman break galaxies
2010
We present first results of a study of the submillimetre (rest frame far-infrared) properties of z ∼3 Lyman Break Galaxies (LBGs) and their lower-redshift counterparts BX/BM galaxies, based on Herschel-SPIRE observations of the Northern field of the Great Observatories Origins Deep Survey (GOODS-N). We use stacking analysis to determine the properties of LBGs well below the current limit of the survey. Although LBGs are not detected individually, stacking the infrared luminous LBGs (those detected with Spitzer at 24 µm) yields a statistically significant submm detection with mean flux S 250 = 5.9±1.4 mJy confirming the power of SPIRE in detecting UV-selected high-redshift galaxies at submillimetre wavelengths. In comparison, the Spitzer 24 µm detected BX/BM galaxies appear fainter with a stacked value of S 250 = 2.7±0.8 mJy. By fitting the Spectral Energy Distributions (SEDs) we derive median infrared luminosities, L IR , of 2.8×10 12 L ⊙ and 1.5×10 11 L ⊙ for z ∼3 LBGs and BX/BMs, respectively. We find that L IR estimates derived from present measurements are in good agreement with those based on UV data for z∼2 BX/BM galaxies, unlike the case for z ∼3 infrared luminous LBGs where the UV underestimates the true L IR . Although sample selection effects may influence this result we suggest that differences in physical properties (such as morphologies, dust distribution and extent of star-forming regions) between z ∼3 LBGs and z∼2 BX/BMs may also play a significant role.
The Astrophysical Journal, 2009
We report on observations of Lyman-break galaxies (LBGs) selected from the Great Observatories Origins Deep Survey (GOODS) at mean redshifts z ∼ 4, 5 and 6 (B 435 -, V 606 -and i 775 -band dropouts, respectively), obtained with the red-sensitive FORS2 spectrograph at the ESO VLT. This program has yielded spectroscopic identifications for 114 galaxies (∼ 60% of the targeted sample), of which 51 are at z ∼ 4, 31 at z ∼ 5, and 32 at z ∼ 6. We demonstrate that 1 Based on observations made at the European Southern Observatory Very Large Telescope, Paranal, Chile (ESO programme 170.A-0788 The Great Observatories Origins Deep Survey: ESO Public Observations of the SST Legacy / HST Treasury / Chandra Deep Field South). Also based on observations obtained with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under NASA contract NAS 5-26555.
Far-infrared-detected Lyman-break galaxies at z ~ 3
Astronomy & Astrophysics, 2013
Lyman-break galaxies (LBGs) represent one of the kinds of star-forming galaxies that are found in the high-redshift universe. The detection of LBGs in the far-infrared (FIR) domain can provide very important clues on their dust attenuation and total star-formation rate (SFR), allowing a more detailed study than has been performed so far. In this work we explore the FIR emission of a sample of 16 LBGs at z ∼ 3 in the GOODS-North and GOODS-South fields that are individually detected in PACS-100 μm or PACS-160 μm. These detections demonstrate the possibility of measuring the dust emission of LBGs at high redshift. We find that PACS-detected LBGs at z ∼ 3 are highly obscured galaxies which belong to the ultra-luminous or hyper-luminous IR galaxy class. Their total SFR cannot be recovered with the dust attenuation factors obtained from their UV continuum slope or their SED-derived dust attenuation employing templates. Both methods underestimate the results for most of the galaxies. Comparing with a sample of PACS-detected LBGs at z ∼ 1, we find evidence that the FIR emission of LBGs might have changed with redshift, in the sense that the dustiest LBGs found at z ∼ 3 have more prominent FIR emission, are dustier for a given UV slope, and have higher SFR for a given stellar mass than the dustiest LBGs found at z ∼ 1.
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.
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.
X-ray properties of lyman break galaxies in the great observatories origins deep survey
Astronomical Journal, 2005
We constrain the X-ray emission properties of Lyman break galaxies (LBGs) at z ≈ 3-6 using the ≈ 2 Ms Chandra Deep Field-North and ≈ 1 Ms Chandra Deep Field-South. Large samples of LBGs were discovered using HST as part of the Great Observatories Origins Deep Survey (GOODS). Deep optical and X-ray imaging over the GOODS fields have allowed us to place the most significant constraints on the X-ray properties of LBGs to date. Mean Xray properties of 449, 1734, 629, and 247 LBGs with z ∼ 3, 4, 5, and 6, respectively, were determined using stacking techniques. When stacked, we detect X-ray emission from LBGs at z ∼ 3 (∼ 7σ) and from an optically bright subset (brightest 25%) of LBGs at z ∼ 4 (∼ 3σ); the latter is the highest redshift detection yet for "normal" galaxies in the X-ray band. The effective exposure times for these stacked observations are ≈ 0.7 and 0.5 Gs, respectively. The derived average rest-frame 2.0-8.0 keV luminosities are 1.5 and 1.4 × 10 41 erg s −1 , respectively. Xray emission from these LBGs is likely due to high mass X-ray binaries (HMXBs) and Type II supernovae; the corresponding star formation rates are ≈ 85-240 M ⊙ yr −1. The X-ray to B-band mean luminosity ratio (L X /L B) at z ∼ 3 is somewhat elevated with respect to that measured for starburst galaxies in the local Universe (significance ∼ 3σ). When stacking full samples of LBGs at z ∼ 4, 5, and 6 we do not obtain significant detections (< 3σ) and derive rest-frame 2.0-8.0 keV luminosity upper limits (3σ) of 0.9, 2.8, and 7.1 × 10 41 erg s −1 , respectively. These upper limits constrain any widespread AGN activity in these objects to be modest at best. Furthermore, we find that ∼ 0.5% of our LBGs from z ≈ 3-6 are detected individually in the Xray band. These LBGs have spectral shapes and luminosities characteristic of moderate-power AGN (e.g., Seyfert galaxies and quasars).
The Astrophysical Journal, 2011
While the Swift satellite is primarily designed to study gamma-ray bursts, its ultraviolet and optical imaging and spectroscopy capabilities are also being used for a variety of scientific programs. In this study, we use the UV/ Optical Telescope (UVOT) instrument on board Swift to discover 0.5 < z < 2 Lyman break galaxies (LBGs). UVOT has covered ∼266 arcmin 2 at >60 ks exposure time, achieving a limiting magnitude of u < 24.5, in the Chandra Deep Field South (CDF-S). Applying UVOT near-ultraviolet color selection, we select 50 UV-dropouts from this UVOT CDF-S data. We match the selected sources with available multiwavelength data from Great Observatories Origins Deep Survey (GOODS) South, Multiwavelength Survey by Yale-Chile, and COMBO-17 to characterize the spectral energy distributions for these galaxies and determine stellar masses, star formation rates (SFRs), and dust attenuations. We compare these properties for LBGs selected in this paper versus z ∼ 3 LBGs and other CDF-S galaxies in the same redshift range (0.5 < z < 2), identified using photometric redshift techniques. The z ∼ 1 LBGs have stellar masses of logM * /M = 9.4 ± 0.6, which is slightly lower than z ∼ 3 LBGs ( logM * /M = 10.2 ± 0.4) and slightly higher compared with the z ∼ 1 CDF-S galaxies ( logM * /M = 8.7 ± 0.7). Similarly, our sample of z ∼ 1 LBGs has SFRs (derived using both ultraviolet and infrared data, where available) of logSFR/(M yr −1 ) = 0.7 ± 0.6, nearly an order of magnitude lower than z ∼ 3 LBGs ( logSFR/M yr −1 = 1.5 ± 0.4), but slightly higher than the comparison z ∼ 1 sample of CDF-S galaxies ( logSFR/M yr −1 = 0.2 ± 0.7). We find that our z ∼ 1 UV-dropouts have A FUV = 2.0 ± 1.0, which is higher than z ∼ 3 LBGs ( A FUV = 1.0 ± 0.5), but similar to the distribution of dust attenuations in the other CDF-S galaxies ( A FUV ∼ 2.8 ± 1.5). Using the GOODS-South multiwavelength catalog of galaxies, we simulate a larger and fainter sample of LBGs to compare their properties with those of the UVOT-selected LBG sample. We conclude that UVOT can be useful for finding and studying the bright end of 0.5 < z < 2.0 LBGs.
The Astrophysical Journal, 2011
We present the final results from our 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 over three independent fields. In particular we report on two newly discovered galaxies at redshift ∼ 6.7 in the NTT deep field: both galaxies show a Lyα emission line with rest-frame EWs of the order 15-20Å and luminosities of 2-4×10 42 ergs −1. We also present the results of ultra-deep observations of a sample of i-dropout galaxies, from which we set a solid upper limit on the fraction of interlopers. Out of the 20 z-dropouts observed we confirm 5 galaxies at 6.7 < z < 7.1. This is systematically below the expectations drawn on the basis of lower redshift observations: in particular there is a significant lack of objects with intermediate Lyα EWs (between 20 and 55Å). We conclude that the trend for the fraction of Lyα emission in LBGs that is constantly increasing from z∼3 to z∼6 is most probably reversed from z ∼ 6 to z∼7. Explaining the observed rapid change in the LAE fraction among the drop-out population with reionization requires a fast evolution of the neutral fraction of hydrogen in the Universe. Assuming that the Universe is completely ionized at z=6 and adopting the semi-analytical models of Dijkstra et al. (2011), we find that our data require a change of the neutral hydrogen fraction of the order ∆χ HI ∼ 0.6 in a time ∆z ∼ 1, provided that the escape fraction does not increase dramatically over the same redshift interval. Subject headings: galaxies: distances and redshifts-galaxies: high-redshift-galaxies: formation * We would like to dedicate this paper in memory of Alan Moorwood, who left us a few days before the paper was submitted. Alan was fundamental to the development of Hawk-I, which enabled this survey and many other important observing programs. He had clear foresight of the instrument's impact on the search for the highest redshift galaxies. More importantly, he always urged us to obtain spectroscopic confirmation of the candidates, and he was eagerly awaiting the results of this effort.