| 1. |
- Berry, Michael, et al.
(författare)
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STACKED REST-FRAME ULTRAVIOLET SPECTRA OF Ly alpha-EMITTING AND CONTINUUM-SELECTED GALAXIES AT 2 < z < 3.5
- 2012
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 749:1, s. 4-
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Tidskriftsartikel (refereegranskat)abstract
- We present properties of individual and composite rest-UV spectra of continuum-and narrowband-selected star-forming galaxies (SFGs) at a redshift of 2 < z < 3.5 discovered by the MUSYC collaboration in the Extended Chandra Deep Field-South. Among our sample of 81 UV-bright SFGs, 59 have R < 25.5, of which 32 have rest-frame equivalent widths of W-Ly alpha > 20 angstrom, the canonical limit to be classified as an Ly alpha-emitting galaxy. We divide our data set into subsamples based on properties that we are able to measure for each individual galaxy: Ly alpha equivalent width, rest-frame UV colors, and redshift. Among our subsample of galaxies with R < 25.5, those with rest frame W-Ly alpha > 20 angstrom have bluer UV continua, weaker low-ionization interstellar absorption lines, weaker C IV absorption, and stronger Si II* nebular emission than those with W-Ly alpha < 20 angstrom. We measure a velocity offset of Delta nu similar to 600 km s(-1) between Ly alpha emission and low-ionization absorption, which does not vary substantially among any of our subsamples. We find that the interstellar component, as opposed to the stellar component, dominates the high-ionization absorption line profiles. We find that the low-and high-ionization Si ionization states have similar kinematic properties, yet the low-ionization absorption is correlated with Ly alpha emission and the high-ionization absorption is not. These trends are consistent with outflowing neutral gas being in the form of neutral clouds embedded in ionized gas as previously suggested by Steidel et al. Moreover, our galaxies with bluer UV colors have stronger Ly alpha emission, weaker low-ionization absorption, and more prominent nebular emission line profiles. From a redshift of 2.7 < z < 3.5 to 2.0 < z < 2.7, our subsample of galaxies with W-Ly alpha < 20 angstrom shows no significant evolution in their physical properties or the nature of their outflows. Among our data set, UV-bright galaxies with W-Ly alpha > 20 angstrom exhibit weaker Ly alpha emission at lower redshifts, although we caution that this could be caused by spectroscopic confirmation of low Ly alpha equivalent width galaxies being harder at z similar to 3 than z similar to 2.
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| 2. |
- Bond, Nicholas A., et al.
(författare)
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EVOLUTION IN THE CONTINUUM MORPHOLOGICAL PROPERTIES OF Ly alpha-EMITTING GALAXIES FROM z=3.1 TO z=2.1
- 2012
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 753:2, s. 95-
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Tidskriftsartikel (refereegranskat)abstract
- We present a rest-frame ultraviolet morphological analysis of 108 z similar or equal to 2.1 Ly alpha emitters (LAEs) in the Extended Chandra Deep Field South and compare it to a similar sample of 171 LAEs at z similar or equal to 3.1. Using Hubble Space Telescope images from the Galaxy Evolution from Morphology and SEDs survey, Great Observatories Origins Deep Survey, and Hubble Ultradeep Field, we measure size and photometric component distributions, where photometric components are defined as distinct clumps of UV-continuum emission. At both redshifts, >80% of LAEs have observed half-light radii < 2 kpc, but the median half-light radius rises from 0.95 +/- 0.04 kpc at z = 3.1 to 1.41 +/- 0.14 kpc at z = 2.1. A similar evolution is seen in the sizes of individual rest-UV components, but there is no evidence for evolution in the number of multi-component systems. In the z = 2.1 sample, we see clear correlations between the size of an LAE and other physical properties derived from its spectral energy distribution (SED). LAEs are found to be larger for galaxies with higher stellar mass, star formation rate, and dust obscuration, but there is no evidence for a trend between equivalent width and half-light radius at either redshift. The presence of these correlations suggests that a wide range of objects are being selected by LAE surveys at z similar or equal to 2, including a significant fraction of objects for which a massive and moderately extended population of old stars underlies the young starburst giving rise to the Ly alpha emission.
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| 3. |
- Bridge, Joanna S., et al.
(författare)
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The Ly alpha Reference Sample. VIII. Characterizing Ly alpha Scattering in Nearby Galaxies
- 2018
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 852:1
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Tidskriftsartikel (refereegranskat)abstract
- We examine the dust geometry and Ly alpha scattering in the galaxies of the Lyman Alpha Reference Sample (LARS), a set of 14 nearby (0.02 < z < 0.2) Ly alpha-emitting and starbursting systems with Hubble Space Telescope Ly alpha, H alpha, and H beta imaging. We find that the global dust properties determined by line ratios are consistent with other studies, with some of the LARS galaxies exhibiting clumpy dust media, while others of them show significantly lower Ly alpha emission compared to their Balmer decrement. With the LARS imaging, we present Ly alpha/H alpha and H alpha/H beta maps with spatial resolutions as low as similar to 40 pc, and use these data to show that in most galaxies, the dust geometry is best modeled by three distinct regions: a central core where dust acts as a screen, an annulus where dust is distributed in clumps, and an outer envelope where Ly alpha photons only scatter. We show that the dust that affects the escape of Ly alpha is more restricted to the galaxies' central regions, while the larger Ly alpha halos are generated by scattering at large radii. We present an empirical modeling technique to quantify how much Ly alpha scatters in the halo, and find that this characteristic scattering distance correlates with the measured size of the Ly alpha halo. We note that there exists a slight anti-correlation between the scattering distance of Ly alpha and global dust properties.
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| 4. |
- Feldmeier, John J., et al.
(författare)
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SEARCHING FOR NEUTRAL HYDROGEN HALOS AROUND z similar to 2.1 AND z similar to 3.1 Ly alpha EMITTING GALAXIES
- 2013
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 776:2, s. 75-
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Tidskriftsartikel (refereegranskat)abstract
- We search for evidence of diffuse Ly alpha emission from extended neutral hydrogen surrounding Ly alpha emitting galaxies (LAEs) using deep narrow-band images of the Extended Chandra Deep Field South. By stacking the profiles of 187 LAEs at z = 2.06, 241 LAEs at z = 3.10, and 179 LAEs at z = 3.12, and carefully performing low-surface brightness photometry, we obtain mean surface brightness maps that reach 9.9, 8.7, and 6.2 x 10(-19) erg cm(-2) s(-1) arcsec(-2) in the emission line. We undertake a thorough investigation of systematic uncertainties in our surface brightness measurements and find that our limits are 5-10 times larger than would be expected from Poisson background fluctuations; these uncertainties are often underestimated in the literature. At z similar to 3.1, we find evidence for extended halos with small-scale lengths of 5-8 kpc in some but not all of our sub-samples. We demonstrate that sub-samples of LAEs with low equivalent widths and brighter continuum magnitudes are more likely to possess such halos. At z similar to 2.1, we find no evidence of extended Ly alpha emission down to our detection limits. Through Monte-Carlo simulations, we also show that we would have detected large diffuse LAE halos if they were present in our data sets. We compare these findings to other measurements in the literature and discuss possible instrumental and astrophysical reasons for the discrepancies.
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| 5. |
- Guaita, Lucia, et al.
(författare)
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Ly alpha-EMITTING GALAXIES AT z=2.1 : STELLAR MASSES, DUST, AND STAR FORMATION HISTORIES FROM SPECTRAL ENERGY DISTRIBUTION FITTING
- 2011
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 733:2, s. 114-
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Tidskriftsartikel (refereegranskat)abstract
- We study the physical properties of 216 z similar or equal to 2.1 Ly alpha-emitting galaxies (LAEs) discovered in an ultra-deep narrow-MUSYC image of the ECDF-S. We fit their stacked spectral energy distribution (SED) using Charlot & Bruzual templates. We consider star formation histories (SFHs) parameterized by the e-folding time parameter tau, allowing for exponentially decreasing (tau > 0), exponentially increasing (tau < 0), and constant star formation rates (SFRs). We estimated the average flux at 5015 angstrom of our LAE sample, finding a non-detection, which translates into negligible He II line emission at z similar or equal to 2.1. In addition to this, the lack of high equivalent width (EW) Ly alpha line objects ruled out the hypothesis of a top-heavy initial mass function in LAEs. The typical LAEs of our sample are characterized by best-fit parameters and 68% confidence intervals of log(M(*)/M(circle dot)) = 8.6[8.4-9.1], E(B - V) = 0.22[0.00-0.31], tau = -0.02[(-4)-18] Gyr, and age(SF) = 0.018[0.009-3] Gyr. Thus, we obtain robust measurements of low stellar mass and dust content, but we cannot place meaningful constraints on the age or SFH of the LAEs. We also calculate the instantaneous SFR to be 35[0.003-170] M(circle dot) yr(-1), with its average over the last 100 Myr before observation giving < SFR >(100) = 4[2-30] M(circle dot) yr(-1). When we compare the results for the same SFH, typical LAEs at z similar or equal to 2.1 appear dustier and show higher instantaneous SFRs than z similar or equal to 3.1 LAEs, while the observed stellar masses of the two samples seem consistent. Because the majority are low-mass galaxies, our typical LAEs appear to occupy the low-mass end of the distribution of star-forming galaxies at z similar or equal to 2. We perform SED fitting on several sub-samples selected based on photometric properties and find that LAE sub-samples at z similar or equal to 2.1 exhibit heterogeneous properties. The typical IRAC-bright, UV-bright, and red LAEs have the largest stellar mass and dust reddening. The typical UV-faint, IRAC-faint, and high EW LAE sub-samples appear less massive (<10(9) M(circle dot)) and less dusty, with E(B - V) consistent with zero.
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| 6. |
- Pirzkal, Norbert, et al.
(författare)
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A Two-dimensional Spectroscopic Study of Emission-line Galaxies in the Faint Infrared Grism Survey (FIGS). I. Detection Method and Catalog
- 2018
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 868:1
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Tidskriftsartikel (refereegranskat)abstract
- We present the results from the application of a two-dimensional emission line detection method, EMission-line two-Dimensional (EM2D), to the near-infrared G102 grism observations obtained with the Wide-Field Camera 3 (WFC3) as part of the Cycle 22 Hubble Space Telescope Treasury Program: the Faint Infrared Grism Survey (FIGS). Using the EM2D method, we have assembled a catalog of emission line galaxies (ELGs) with resolved star formation from each of the four FIGS fields. Not only can one better assess the global properties of ELGs, but the EM2D method allows for the analysis and improved study of the individual emission-line region within each galaxy. This paper includes a description of the methodology, advantages, and the first results of the EM2D method applied to ELGs in FIGS. The advantage of 2D emission line measurements includes significant improvement of galaxy redshift measurements, approaching the level of accuracy seen in high-spectral-resolution data, but with greater efficiency; and the ability to identify and measure the properties of multiple sites of star formation and over scales of similar to 1 kpc within individual galaxies out to z similar to 4. The EM2D method also significantly improves the reliability of high-redshift (z similar to 7) Ly alpha detections. Coupled with the wide field of view and high efficiency of space-based grism observations, EM2D provides a noteworthy improvement on the physical parameters that can be extracted from grism observations.
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| 7. |
- Pirzkal, Norbert, et al.
(författare)
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FIGS-Faint Infrared Grism Survey : Description and Data Reduction
- 2017
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 846:1
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Tidskriftsartikel (refereegranskat)abstract
- The Faint Infrared Grism Survey (FIGS) is a deep Hubble Space Telescope (HST) WFC3/IR (Wide Field Camera 3 Infrared) slitless spectroscopic survey of four deep fields. Two fields are located in the Great Observatories Origins Deep Survey-North (GOODS-N) area and two fields are located in the Great Observatories Origins Deep Survey-South (GOODS-S) area. One of the southern fields selected is the Hubble Ultra Deep Field. Each of these four fields were observed using the WFC3/G102 grism (0.8 mu m-1.15 mu m continuous coverage) with a total exposure time of 40 orbits (approximate to 100 kilo-seconds) per field. This reaches a 3 sigma continuum depth of approximate to 26 AB magnitudes and probes emission lines to similar to 10(-17) erg s(-1) cm(-2). This paper details the four FIGS fields and the overall observational strategy of the project. A detailed description of the Simulation Based Extraction (SBE) method used to extract and combine over 10,000 spectra of over 2000 distinct sources brighter than m(F105W) = 26.5 mag is provided. High fidelity simulations of the observations is shown to significantly improve the background subtraction process, the spectral contamination estimates, and the final flux calibration. This allows for the combination of multiple spectra to produce a final high quality, deep, 1D spectra for each object in the survey.
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| 8. |
- Sandberg, Andreas, 1985-
(författare)
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Observing Lyman alpha emitters - How does Lyman alpha escape from galaxies?
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Lyman alpha (Lyα) emission line has grown to become one of the most successful tools for finding galaxies at high redshift. At redshifts corresponding to the early cosmic times of reionization and primeval galaxy formation, the wavelength of Lyα is still accessible with ground-based facilities. Lyα is a resonance line which undergoes a complicated radiative transfer process through the neutral gas inside galaxies. This process is still not fully understood. The precise distribution and kinematics of stars, gas and dust all seem to affect the amount of Lyα that eventually escapes the galaxy. Observational studies of Lyα emitting galaxies are necessary for understanding this process in detail.From previous observations and simulations, it is evident that outflows of neutral gas can facilitate the escape of Lyα photons, as the Doppler effect shifts the frequency out of resonance. In Paper I we explore the connection between Lyα escape and outflows of neutral gas as measured with the Na D absorption feature in two nearby Lyα emitting galaxies. We find suprisingly little evidence for such a connection, and speculate how the Na D absorption is perhaps not measuring the velocity of the gas which is the most important for Lyα escape.Papers II and III address LARS - the Lyman Alpha Reference Sample - a project in which 14 nearby galaxies and their Lyα emission are studied in detail using the Hubble Space Telescope. The two papers describe how we directly image the Lyα emission and absorption in these galaxies, and relate it to their physical properties. We find that Lyα escape is more probable in galaxies with younger age, and lower mass, dust content and instantaneous star formation rate, whereas the total Lyα luminosity appears to be independent of these factors.Papers IV and V then turn to higher redshifts, exploring Lyα and Lyman Continuum escape at z ∼ 2. In Paper IV we find 25 Lyα-emitting galaxies (LAEs) using the photometric narrow-band technique, and we explore their multi-wavelength properties. Our results are well in line with similar studies at this redshift. We also find several luminous infrared galaxies (LIRGs) in the sample, which may seem surprising given their high dust content, but we also review similar previous findings in the literature.Paper V describes the method of using Hα-emitting galaxies (HAEs) in order to accurately ascertain the Lyman Continuum escape fraction from a galaxy population, a number which is crucial for the understanding of the role of galaxies during the epoch of reionization. An Hα-selected sample is less biased towards dust-free systems than UV-selected samples, which are typically used for this type of study. We also use the method on 10 strongly clustered HAEs and constrain the Lyman Continuum escape fraction to <24%, but stress that this number is strongly affected by cosmic variance and that further studies of HAEs could provide very robust constraints on the escape fraction.
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| 9. |
- Vargas, Carlos J., et al.
(författare)
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TO STACK OR NOT TO STACK : SPECTRAL ENERGY DISTRIBUTION PROPERTIES OF Ly alpha-EMITTING GALAXIES AT z=2.1
- 2014
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 783:1, s. 26-
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Tidskriftsartikel (refereegranskat)abstract
- We use the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey (CANDELS) GOODS-S multi-wavelength catalog to identify counterparts for 20 Ly alpha emitting (LAE) galaxies at z = 2.1. We build several types of stacked spectral energy distributions (SEDs) of these objects. We combine photometry to form average and median flux-stacked SEDs, and postage-stamp images to form average and median image-stacked SEDs. We also introduce scaled flux stacks that eliminate the influence of variation in overall brightness. We use the SED fitting code SpeedyMC to constrain the physical properties of individual objects and stacks. Our LAEs at z = 2.1 have stellar masses ranging from 2 x 10(7) M-circle dot to 8 x 10(9) M-circle dot (median = 3 x 10(8) M-circle dot), ages ranging from 4 Myr to 500 Myr (median = 100 Myr), and E(B - V) between 0.02 and 0.24 (median = 0.12). Although still low, this represents significantly more dust reddening than has been reported for LAEs at higher redshifts. We do not observe strong correlations between Ly alpha equivalent width (EW) and age or E(B - V). The Ly alpha radiative transfer (q) factors of our sample are predominantly close to one and do not correlate strongly with EW or E(B - V). The absence of strong correlations with EW or q implies that Ly alpha radiative transfer is highly anisotropic and/or prevents Ly alpha photons from scattering in dusty regions. The SED parameters of the flux stacks match the average and median values of the individual objects, with the flux-scaled median SED performing best with uncertainties reduced by a factor of two. Median image-stacked SEDs provide a poor representation of the median individual object, and none of the stacking methods capture the large dispersion of LAE properties.
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| 10. |
- Zheng, Zhen-Ya, et al.
(författare)
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X-RAY CONSTRAINTS ON THE Ly alpha ESCAPE FRACTION
- 2012
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 746:1
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Tidskriftsartikel (refereegranskat)abstract
- We have co-added the X-ray flux of all known Lya emitters (LAEs) in the 4 Ms Chandra Deep Field South (CDF-S) region, achieving the tightest upper limits yet on the X-ray to Lya ratio. We use the X-ray data to place sensitive upper limits on the average unobscured star formation rate (SFRX) in these galaxies. A very small fraction of Lya galaxies in the field are individually detected in the X-rays, implying a low fraction of active galactic nucleus activity. After excluding the few X-ray-detected LAEs, we stack the undetected LAEs located in the 4 Ms CDF-S data and 250 ks Extended CDF-S (ECDF-S) data, and compute a 1 sigma upper limit on SFRX < 1.6, 14, 28, 28, 140, 440, 880M(circle dot) yr(-1) for LAEs located at z similar to 0.3 and z = 2.1, 3.1, 3.2, 4.5, 5.7, and 6.5, respectively. The upper limit of SFRX in LAEs can be then compared to SFRLy alpha derived from Lya line and thus can constrain on the Lya escape fraction (f(Ly alpha)(Esc)). The f(Ly alpha)(Esc) from X-ray at z similar to 0.3 is substantially larger than that from UV or H alpha. Three X-ray-detected LAE galaxies at z similar to 0.3 show f(Ly alpha)(Esc) similar to 3%-22%, and the average Ly alpha escape fraction from stacking the X-ray-undetected LAEs show f(Ly alpha)(Esc) > 28% at 3 sigma significance level at the same redshift. We derive a lower limit on f(Ly alpha)(Esc) > 14% (84% confidence level, 1 sigma lower limit) for LAEs at redshift z similar to 2.1 and z similar to 3.1-3.2. At z > 4, the current LAE samples are not of sufficient size to constrain SFRX well. By averaging all the LAEs at z > 2, the X-ray non-detection constrains f(Ly alpha)(Esc)17% (84% confidence level, 1 sigma lower limit), and rejects f(Ly alpha)(Esc) < 5.7% at the 99.87% confidence level from 2.1 < z < 6.5.
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