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Atek H.,Spitzer Science Center | Siana B.,California Institute of Technology | Scarlata C.,University of Minnesota | Malkan M.,University of California at Los Angeles | And 12 more authors.
Astrophysical Journal | Year: 2011

The WFC3 Infrared Spectroscopic Parallel Survey uses the Hubble Space Telescope (HST) infrared grism capabilities to obtain slitless spectra of thousands of galaxies over a wide redshift range including the peak of star formation history of the universe. We select a population of very strong emission-line galaxies with rest-frame equivalent widths (EWs) higher than 200 . A total of 176 objects are found over the redshift range 0.35 < z < 2.3 in the 180 arcmin2 area that we have analyzed so far. This population consists of young and low-mass starbursts with high specific star formation rates (sSFR). After spectroscopic follow-up of one of these galaxies with Keck/Low Resolution Imaging Spectrometer, we report the detection at z = 0.7 of an extremely metal-poor galaxy with 12 + log(O/H) =7.47 0.11. After estimating the active galactic nucleus fraction in the sample, we show that the high-EW galaxies have higher sSFR than normal star-forming galaxies at any redshift. We find that the nebular emission lines can substantially affect the total broadband flux density with a median brightening of 0.3 mag, with some examples of line contamination producing brightening of up to 1 mag. We show that the presence of strong emission lines in low-z galaxies can mimic the color-selection criteria used in the z 8 dropout surveys. In order to effectively remove low-redshift interlopers, deep optical imaging is needed, at least 1 mag deeper than the bands in which the objects are detected. Without deep optical data, most of the interlopers cannot be ruled out in the wide shallow HST imaging surveys. Finally, we empirically demonstrate that strong nebular lines can lead to an overestimation of the mass and the age of galaxies derived from fitting of their spectral energy distribution (SED). Without removing emission lines, the age and the stellar mass estimates are overestimated by a factor of 2 on average and up to a factor of 10 for the high-EW galaxies. Therefore, the contribution of emission lines should be systematically taken into account in SED fitting of star-forming galaxies at all redshifts. © 2011. The American Astronomical Society. All rights reserved. Source

Atek H.,Spitzer Science Center | Malkan M.,University of California at Los Angeles | McCarthy P.,Carnegie Institution for Science | Teplitz H.I.,Infrared Processing and Analysis Center | And 11 more authors.
Astrophysical Journal | Year: 2010

We present the WFC3 Infrared Spectroscopic Parallel (WISP) Survey. WISP is obtaining slitless, near-infrared grism spectroscopy of ∼90 independent, high-latitude fields by observing in the pure-parallel mode with the Wide Field Camera Three on the Hubble Space Telescope for a total of ∼250 orbits. Spectra are obtained with the G102 (λ = 0.8-1.17 μm, R ∼ 210) and G141 grisms (λ = 1.11-1.67 μm, R ∼ 130), together with direct imaging in the J and H bands (F110W and F140W, respectively). In the present paper, we present the first results from 19 WISP fields, covering approximately 63 arcmin2. For typical exposure times (∼6400 s in G102 and ∼2700 s in G141), we reach 5σ detection limits for emission lines of f ∼ 5 × 10 -17 erg s-1 cm-2 for compact objects. Typical direct imaging 5σ limits are 26.3 and 26.1 mag. (AB) in F110W and F140W, respectively. Restricting ourselves to the lines measured with the highest confidence, we present a list of 328 emission lines, in 229 objects, in a redshift range 0.3 < z < 3. The single-line emitters are likely to be a mix of Hα and [O III]5007,4959 Å, with Hα predominating. The overall surface density of high-confidence emission-line objects in our sample is approximately 4 per arcmin2. These first fields show high equivalent width sources, active galactic nucleus, and post-starburst galaxies. The median observed star formation rate (SFR) of our Hα-selected sample is 4 M⊙ yr-1. At intermediate redshifts, we detect emission lines in galaxies as faint as H140 ∼ 25, or M R < - 19, and are sensitive to SFRs down to less than 1M ⊙ yr-1. The slitless grisms on WFC3 provide a unique opportunity to study the spectral properties of galaxies much fainter than L* at the peak of the galaxy assembly epoch. © 2010. The American Astronomical Society. Source

Lyubenova M.,ESO | Kuntschner H.,Space Telescope European Coordinating Facility | Rejkuba M.,ESO | Silva D.R.,National Optical Astronomy Observatory | And 3 more authors.
Astronomy and Astrophysics | Year: 2010

Current stellar population models have arguably the largest uncertainties in the near-IR wavelength range, partly due to a lack of large and well calibrated empirical spectral libraries. In this paper we present a project whose aim it is to provide the first library of luminosity weighted integrated near-IR spectra of globular clusters to be used to test the current stellar population models and serve as calibrators for future ones. Our pilot study presents spatially integrated K-band spectra of three old (=10 Gyr) and metal poor ([Fe/H] ~ -1.4), and three intermediate age (12 Gyr) and more metal rich ([Fe/H] ~ -0.4) globular clusters in the LMC. We measured the line strengths of the Na i, Cai and 12CO(20) absorption features. The Na i index decreases with increasing age and decreasing metallicity of the clusters. The DCO index, used to measure the 12CO(20) line strength, is significantly reduced by the presence of carbon-rich TP-AGB stars in the globular clusters with age ~1 Gyr. This is in contradiction to the predictions of the stellar population models of Maraston (2005, MNRAS, 362, 799). We find that this disagreement is due to the different CO absorption strength of carbon-rich Milky Way TP-AGB stars used in the models and the LMC carbon stars in our sample. For globular clusters with age ≥2 Gyr we find DCO index measurements consistent with the model predictions. © ESO, 2010. Source

Oosterloo T.,Netherlands Institute for Radio Astronomy | Oosterloo T.,University of Groningen | Morganti R.,Netherlands Institute for Radio Astronomy | Morganti R.,University of Groningen | And 14 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2010

We present an analysis of deep Westerbork Synthesis Radio Telescope observations of the neutral hydrogen in 33 nearby early-type galaxies selected from a representative sample studied earlier at optical wavelengths with the SAURON integral-field spectrograph. This is the deepest homogeneous set of H-i imaging data available for this class of objects. The sample covers both field environments and the Virgo cluster. Our analysis shows that gas accretion plays a role in the evolution of field early-type galaxies, but less so for those in clusters.The H-i properties of SAURON early-type galaxies strongly depend on environment. For detection limits of a few times 106- M-, H-i is detected in about 2/3 of the field galaxies, while <10 per cent of the Virgo objects are detected. In about half of the detections, the H-i forms a regularly rotating disc or ring. In many galaxies unsettled tails and clouds are seen. All H-i discs have counterparts of ionized gas, and inner H-i discs are also detected in molecular gas. The cold interstellar medium (ISM) in the central regions is dominated by molecular gas (). Assuming our sample is representative, we conclude that accretion of H-i is very common for field early-type galaxies, but the amount of material involved is usually small and the effects on the host galaxy are, at most, subtle. Cluster galaxies appear not to accrete H-i, or the accreted material gets removed quickly by environmental effects. The relation between H-i and stellar population is complex. The few galaxies with a significant young sub-population all have inner gas discs, but for the remaining galaxies there is no trend between stellar population and H-i properties. A number of early-type galaxies are very gas rich, but only have an old population. The stellar populations of field galaxies are typically younger than those in Virgo. This is likely related to differences in accretion history. There is no obvious overall relation between gas H-i content and global dynamical characteristics except that the fastest rotators all have an H-i disc. This confirms that if fast and slow rotators are the result of different evolution paths, this is not strongly reflected in the current H-i content. In about 50 per cent of the galaxies we detect a central radio continuum source. In many objects this emission is from a low-luminosity active galactic nucleus (AGN), and in some it is consistent with the observed star formation. Galaxies with H-i in the central regions are more likely detected in continuum. This is due to a higher probability for star formation to occur in such galaxies and not to H-i-related AGN fuelling. © 2010 The Authors. Journal compilation © 2010 RAS. Source

Straughn A.N.,Goddard Space Flight Center | Kuntschner H.,Space Telescope European Coordinating Facility | Kummel M.,Space Telescope European Coordinating Facility | Walsh J.R.,Space Telescope European Coordinating Facility | And 28 more authors.
Astronomical Journal | Year: 2011

We present grism spectra of emission-line galaxies (ELGs) from 0.6 to 1.6μm from the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope. These new infrared grism data augment previous optical Advanced Camera for Surveys G800L 0.6-0.95μm grism data in GOODS-South from the PEARS program, extending the wavelength coverage well past the G800L red cutoff. The Early Release Science (ERS) grism field was observed at a depth of two orbits per grism, yielding spectra of hundreds of faint objects, a subset of which is presented here. ELGs are studied via the Hα, [Oiii], and [O ii] emission lines detected in the redshift ranges 0.2 ≲ z ≲ 1.4, 1.2 ≲ z ≲ 2.2, and 2.0 ≲ z ≲ 3.3, respectively, in the G102 (0.8-1.1μm; R ≃ 210) and G141 (1.1-1.6μm; R ≃ 130) grisms. The higher spectral resolution afforded by the WFC3 grisms also reveals emission lines not detectable with the G800L grism (e.g., [S ii] and [S iii] lines). From these relatively shallow observations, line luminosities, star formation rates, and grism spectroscopic redshifts are determined for a total of 48 ELGs to mAB(F098M) ≃ 25 mag. Seventeen GOODS-South galaxies that previously only had photometric redshifts now have new grism-spectroscopic redshifts, in some cases with large corrections to the photometric redshifts (Δz ≃ 0.3-0.5). Additionally, one galaxy had no previously measured redshift but now has a secure grism-spectroscopic redshift, for a total of 18 new GOODS-South spectroscopic redshifts. The faintest source in our sample has a magnitude mAB(F098M)= 26.9 mag. The ERS grism data also reflect the expected trend of lower specific star formation rates for the highest mass galaxies in the sample as a function of redshift, consistent with downsizing and discovered previously from large surveys. These results demonstrate the remarkable efficiency and capability of the WFC3 NIR grisms for measuring galaxy properties to faint magnitudes and redshifts to z ≲ 2. © 2011. The American Astronomical Society. All rights reserved. Printed in the U.S.A. Source

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