| 1. |
- Bagley, Micaela B., et al.
(författare)
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A High Space Density of Luminous Ly alpha Emitters at z similar to 6.5
- 2017
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 837:1
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Tidskriftsartikel (refereegranskat)abstract
- We present the results of a systematic search for Ly alpha emitters (LAEs) at 6 less than or similar to z less than or similar to 7.6 using the HST WFC3 Infrared Spectroscopic Parallel (WISP) Survey. Our total volume over this redshift range is similar to 8 x 10(5) Mpc(3), comparable to many of the narrowband surveys despite their larger area coverage. We find two LAEs at z = 6.38 and 6.44 with line luminosities of L-Lya similar to 4.7 x 10(43) erg s(-1), putting them among the brightest LAEs discovered at these redshifts. Taking advantage of the broad spectral coverage of WISP, we are able to rule out almost all lower-redshift contaminants. The WISP LAEs have a high number density of 7.7 x 10(-6) Mpc (3). We argue that the LAEs reside in megaparsec-scale ionized bubbles that allow the Ly alpha photons to redshift out of resonance before encountering the neutral intergalactic medium. We discuss possible ionizing sources and conclude that the observed LAEs alone are not sufficient to ionize the bubbles.
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| 2. |
- Kuschel, Maxwell, et al.
(författare)
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Investigating the Dominant Environmental Quenching Process in UVCANDELS/COSMOS Groups
- 2023
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 947:1
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Tidskriftsartikel (refereegranskat)abstract
- We explore how the fraction of quenched galaxies changes in groups of galaxies with respect to the distance to the center of the group, redshift, and stellar mass to determine the dominant process of environmental quenching in 0.2 < z < 0.8 groups. We use new UV data from the UVCANDELS project in addition to existing multiband photometry to derive new galaxy physical properties of the group galaxies from the zCOSMOS 20 k group catalog. Limiting our analysis to a complete sample of log (M*/M⊙) > 10.56 group galaxies, we find that the probability of being quenched increases slowly with decreasing redshift, diverging from the stagnant field galaxy population. A corresponding analysis on how the probability of being quenched increases with time within groups suggests that the dominant environmental quenching process is characterized by slow (∼Gyr) timescales. We find a quenching time of approximately Gyr, consistent with the slow processes of strangulation and delayed-then-rapid quenching although more data are needed to confirm this result.
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| 3. |
- Mehta, Vihang, et al.
(författare)
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A Spatially Resolved Analysis of Star Formation Burstiness by Comparing UV and Hα in Galaxies at z ∼ 1 with UVCANDELS
- 2023
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 952:2
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Tidskriftsartikel (refereegranskat)abstract
- The UltraViolet imaging of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey Fields (UVCANDELS) program provides Hubble Space Telescope (HST)/UVIS F275W imaging for four CANDELS fields. We combine this UV imaging with existing HST/near-IR grism spectroscopy from 3D-HST+AGHAST to directly compare the resolved rest-frame UV and Hα emission for a sample of 979 galaxies at 0.7 < z < 1.5, spanning a range in stellar mass of 108−11.5M⊙. Using a stacking analysis, we perform a resolved comparison between homogenized maps of rest-UV and Hα to compute the average UV-to-Hα luminosity ratio (an indicator of burstiness in star formation) as a function of galactocentric radius. We find that galaxies below stellar mass of ∼109.5M⊙, at all radii, have a UV-to-Hα ratio higher than the equilibrium value expected from constant star formation, indicating a significant contribution from bursty star formation. Even for galaxies with stellar mass ≳109.5M⊙, the UV-to-Hα ratio is elevated toward their outskirts (R/Reff > 1.5), suggesting that bursty star formation is likely prevalent in the outskirts of even the most massive galaxies, but is likely overshadowed by their brighter cores. Furthermore, we present the UV-to-Hα ratio as a function of galaxy surface brightness, a proxy for stellar mass surface density, and find that regions below ∼107.5M⊙ kpc−2 are consistent with bursty star formation, regardless of their galaxy stellar mass, potentially suggesting that local star formation is independent of global galaxy properties at the smallest scales. Last, we find galaxies at z > 1.1 to have bursty star formation, regardless of radius or surface brightness.
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| 4. |
- Rutkowski, Michael J., et al.
(författare)
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LYMAN CONTINUUM ESCAPE FRACTION OF STAR-FORMING DWARF GALAXIES AT z similar to 1
- 2016
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 819:1
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Tidskriftsartikel (refereegranskat)abstract
- To date, no direct detection of Lyman continuum emission has been measured for intermediate-redshift (z similar to 1) star-forming galaxies. We combine Hubble Space Telescope grism spectroscopy with GALEX UV and ground-based optical imaging to extend the search for escaping Lyman continuum to a large (similar to 600) sample of z similar to 1 low-mass (log((M) over bar) similar or equal to 9.3M(circle dot)), moderately star-forming ((Psi) over bar less than or similar to 10M(circle dot) yr(-1)) galaxies selected initially on H alpha emission. The characteristic escape fraction of LyC from star-forming galaxies (SFGs) that populate this parameter space remains weakly constrained by previous surveys, but these faint (sub-L-star) SFGs are assumed to play a significant role in the reionization of neutral hydrogen in the intergalactic medium (IGM) at high redshift z > 6. We do not make an unambiguous detection of escaping LyC radiation from this z similar to 1 sample, individual non-detections to constrain the absolute Lyman continuum escape fraction, f(esc) < 2.1% (3 sigma). We measure an upper limit of f(esc) < 9.6% from a sample of SFGs selected on high H alpha equivalent width (EW > 200 angstrom), which are thought to be close analogs of high redshift sources of reionization. For reference, we also present an emissivity-weighted escape fraction that is useful for measuring the general contribution SFGs to the ionizing UV background. In the discussion, we consider the implications of these intermediate redshift constraints for the reionization of hydrogen in the IGM at high (z > 6) redshift. If we assume our z similar to 1 SFGs, for which we measure this emissivity-weighted f(esc), are analogs to the high redshift sources of reionization, we find it is difficult to reconcile reionization by faint (MUV less than or similar to -13) SFGs with a low escape fraction (f(esc) < 3%), with constraints from independent high redshift observations. If f(esc) evolves with redshift, reionization by SFGs may be consistent with observations from Planck.
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| 5. |
- Rutkowski, Michael J., et al.
(författare)
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The Lyman Continuum Escape Fraction of Emission Line-selected z similar to 2.5 Galaxies Is Less Than 15%
- 2017
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 841:2
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Tidskriftsartikel (refereegranskat)abstract
- Recent work suggests that strong emission line, star-forming galaxies (SFGs) may be significant Lyman continuum leakers. We combine archival Hubble Space Telescope broadband ultraviolet and optical imaging (F275W and F606W, respectively) with emission line catalogs derived from WFC3 IR G141 grism spectroscopy to search for escaping Lyman continuum (LyC) emission from homogeneously selected z similar to 2.5 SFGs. We detect no escaping Lyman continuum from SFGs selected on [O II] nebular emission (N = 208) and, within a narrow redshift range, on [O III]/[O II]. We measure 1 sigma upper limits to the LyC escape fraction relative to the non-ionizing UV continuum from [O II] emitters, f(esc) less than or similar to 5.6%, and strong [O III]/[O II] > 5 ELGs, f(esc) less than or similar to 14.0%. Our observations are not deep enough to detect f(esc) similar to 10% typical of low-redshift Lyman continuum emitters. However, we find that this population represents a small fraction of the star-forming galaxy population at z similar to 2. Thus, unless the number of extreme emission line galaxies grows substantially to z greater than or similar to 6, such galaxies may be insufficient for reionization. Deeper survey data in the rest-frame ionizing UV will be necessary to determine whether strong line ratios could be useful for pre-selecting LyC leakers at high redshift.
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| 6. |
- Stark, Daniel P., et al.
(författare)
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Ultraviolet emission lines in young low-mass galaxies at z similar or equal to 2 : physical properties and implications for studies at z > 7
- 2014
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 445:3, s. 3200-3220
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Tidskriftsartikel (refereegranskat)abstract
- We present deep spectroscopy of 17 very low mass (M* similar or equal to 2.0 x 10(6)-1.4 x 10(9) M-circle dot) and low luminosity (M-UV similar or equal to -13.7 to -19.9) gravitationally lensed galaxies in the redshift range z similar or equal to 1.5-3.0. Deep rest-frame ultraviolet spectra reveal large equivalent width emission from numerous emission lines (N IV], O III], C IV, Si III], C III]) which are rarely seen in individual spectra of more massive star-forming galaxies. C III] is detected in 16 of 17 low-mass star-forming systems with rest-frame equivalent widths as large as 13.5 angstrom. Nebular C (IV) emission is present in the most extreme C III] emitters, requiring an ionizing source capable of producing a substantial component of photons with energies in excess of 47.9 eV. Photoionization models support a picture whereby the large equivalent widths are driven by the increased electron temperature and enhanced ionizing output arising from metal-poor gas and stars (0.04-0.13 Z(circle dot)), young stellar populations (6-50 Myr), and large ionization parameters (log U = -2.16 to -1.84). The young ages implied by the emission lines and continuum spectral energy distributions (SEDs) indicate that the extreme line emitters in our sample are in the midst of a significant upturn in their star formation activity. The low stellar masses, blue UV colours, and large specific star formation rates of our sample are similar to those of typical z greater than or similar to 6 galaxies. Given the strong attenuation of Ly alpha in z greater than or similar to 6 galaxies, we suggest that C III] is likely to provide our best probe of early star-forming galaxies with ground-based spectrographs and one off the most efficient means of confirming z greater than or similar to 10 galaxies with the James Webb Space Telescope.
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