The WFC3 Infrared Spectroscopic Parallel (WISP) Survey

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 Wide Field Camera-3 on the Hubble Space Telescope for a total of ~ 250 orbits. Spectra are obtained with the G102 (lambda=0.8-1.17 microns, R ~ 210) and G141 grisms (lambda=1.11-1.67 microns, 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 square arc minutes. For typical exposure times (~ 6400 sec in G102 and ~ 2700 sec in G141), we reach 5-sigma detection limits for emission lines of 5 x 10^(-17) ergs s^(-1) cm^(-2) for compact objects. Typical direct imaging 5sigma-limits are 26.8 and 25.0 magnitudes (AB) in F110W and F140W, respectively. Restricting ourselves to the lines measured with 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 Halpha and [OIII]5007,4959 A, with Halpha predominating. The overall surface density of high-confidence emission-line objects in our sample is approximately 4 per arcmin^(2).These first fields show high equivalent width sources, AGN, and post starburst galaxies. The median observed star formation rate of our Halpha selected sample is 4 Msol/year. At intermediate redshifts, we detect emission lines in galaxies as faint as H_140 ~ 25, or M_R < -19, and are sensitive to star formation rates down to less than 1 Msol/year. 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.Comment: 15 pages, 12 figures, submitted to Ap

IRAC Excess in Distant Star-Forming Galaxies: Tentative Evidence for the 3.3μ\mum Polycyclic Aromatic Hydrocarbon Feature ?

We present evidence for the existence of an IRAC excess in the spectral energy distribution (SED) of 5 galaxies at 0.6<z<0.9 and 1 galaxy at z=1.7. These 6 galaxies, located in the Great Observatories Origins Deep Survey field (GOODS-N), are star forming since they present strong 6.2, 7.7, and 11.3 um polycyclic aromatic hydrocarbon (PAH) lines in their Spitzer IRS mid-infrared spectra. We use a library of templates computed with PEGASE.2 to fit their multiwavelength photometry and derive their stellar continuum. Subtraction of the stellar continuum enables us to detect in 5 galaxies a significant excess in the IRAC band pass where the 3.3 um PAH is expected. We then assess if the physical origin of the IRAC excess is due to an obscured active galactic nucleus (AGN) or warm dust emission. For one galaxy evidence of an obscured AGN is found, while the remaining four do not exhibit any significant AGN activity. Possible contamination by warm dust continuum of unknown origin as found in the Galactic diffuse emission is discussed. The properties of such a continuum would have to be different from the local Universe to explain the measured IRAC excess, but we cannot definitively rule out this possibility until its origin is understood. Assuming that the IRAC excess is dominated by the 3.3 um PAH feature, we find good agreement with the observed 11.3 um PAH line flux arising from the same C-H bending and stretching modes, consistent with model expectations. Finally, the IRAC excess appears to be correlated with the star-formation rate in the galaxies. Hence it could provide a powerful diagnostic for measuring dusty star formation in z>3 galaxies once the mid-infrared spectroscopic capabilities of the James Webb Space Telescope become available.Comment: 25 pages, 4 figures, accepted by Ap

Far-ultraviolet imaging of the Hubble Deep Field-North: Star formation in normal galaxies at z < 1

We present far-ultraviolet (FUV) imaging of the Hubble Deep Field-North (HDF-N) taken with the Solar Blind Channel of the Advanced Camera for Surveys (ACS SBC) and the FUV MAMA detector of the Space Telescope Imaging Spectrograph onboard the Hubble Space Telescope. The full WFPC2 deep field has been observed at 1600 Å. We detect 134 galaxies and one star down to a limit of FUV_(AB) ~ 29. All sources have counterparts in the WFPC2 image. Redshifts (spectroscopic or photometric) for the detected sources are in the range 0 < z < 1. We find that the FUV galaxy number counts are higher than those reported by GALEX, which we attribute at least in part to cosmic variance in the small HDF-N field of view. Six of the 13 Chandra sources at z < 0.85 in the HDF-N are detected in the FUV, and those are consistent with starbursts rather than active galactic nuclei. Cross-correlating with Spitzer sources in the field, we find that the FUV detections show general agreement with the expected L_(IR)/L_(UV) versus β relationship. We infer star formation rates (SFRs), corrected for extinction using the UV slope, and find a median value of 0.3 M_☉ yr^(-1) for FUV-detected galaxies, with 75% of detected sources having SFR < 1 M_☉ yr^(-1). Examining the morphological distribution of sources, we find that about half of all FUV-detected sources are identified as spiral galaxies. Half of morphologically selected spheroid galaxies at z < 0.85 are detected in the FUV, suggesting that such sources have had significant ongoing star formation in the epoch since z ~ 1

Strange Quarks Nuggets in Space: Charges in Seven Settings

We have computed the charge that develops on an SQN in space as a result of balance between the rates of ionization by ambient gammas and capture of ambient electrons. We have also computed the times for achieving that equilibrium and binding energy of the least bound SQN electrons. We have done this for seven different settings. We sketch the calculations here and give their results in the Figure and Table II; details are in the Physical Review D.79.023513 (2009).Comment: Six pages, one figure. To appear in proceedings of the 2008 UCLA coference on dark matter and dark energ

The Hubble Space Telescope GOODS NICMOS Survey: overview and the evolution of massive galaxies at 1.5 < z < 3

We present the details and early results from a deep near-infrared survey utilizing the NICMOS instrument on the Hubble Space Telescope centred around massive M_* > 10^(11) M_⊙ galaxies at 1.7 10^(11) M_⊙, whereby we find an increase of a factor of 8 between z= 3 and 1.5, demonstrating that this is an epoch when massive galaxies establish most of their stellar mass. We also provide an overview of the evolutionary properties of these galaxies, such as their merger histories, and size evolution

Spitzer infrared spectrometer 16μm observations of the GOODS fields

We present Spitzer 16μm imaging of the Great Observatories Origins Deep Survey (GOODS) fields. We survey 150 arcmin^2 in each of the two GOODS fields (North and South), to an average 3σ depth of 40 and 65 μJy, respectively. We detect ~1300 sources in both fields combined. We validate the photometry using the 3–24μm spectral energy distribution of stars in the fields compared to Spitzer spectroscopic templates. Comparison with ISOCAM and AKARI observations in the same fields shows reasonable agreement, though the uncertainties are large. We provide a catalog of photometry, with sources cross-correlated with available Spitzer, Chandra, and Hubble Space Telescope data. Galaxy number counts show good agreement with previous results from ISOCAM and AKARI with improved uncertainties. We examine the 16–24μm flux ratio and find that for most sources it lies within the expected locus for starbursts and infrared luminous galaxies. A color cut of S_(16)/S_(24) > 1.4 selects mostly sources which lie at 1.1 < z < 1.6, where the 24μm passband contains both the redshifted 9.7 μm silicate absorption and the minimum between polycyclic aromatic hydrocarbon emission peaks. We measure the integrated galaxy light of 16μm sources and find a lower limit on the galaxy contribution to the extragalactic background light at this wavelength to be 2.2 ± 0.2 nW m^(−2) sr^(−1)

Measurement of [OIII] Emission in Lyman Break Galaxies

Measurements of [OIII] emission in Lyman Break galaxies (LBGs) at z>3 are presented. Four galaxies were observed with narrow-band filters using the Near-IR Camera on the Keck I 10-m telescope. A fifth galaxy was observed spectroscopically during the commissioning of NIRSPEC, the new infrared spectrometer on Keck II. The emission-line spectrum is used to place limits on the metallicity. Comparing these new measurements with others available from the literature, we find that strong oxygen emission in LBGs may suggest sub-solar metallicity for these objects. The [OIII]5007 line is also used to estimate the star formation rate (SFR) of the LBGs. The inferred SFRs are higher than those estimated from the UV continuum, and may be evidence for dust extinction.Comment: 25 pages, including 6 figures. Accepted for publication in Ap

LBT and Spitzer Spectroscopy of Star-Forming Galaxies at 1 < z < 3: Extinction and Star Formation Rate Indicators

We present spectroscopic observations in the rest-frame optical and near- to mid-infrared wavelengths of four gravitationally lensed infrared (IR) luminous star-forming galaxies at redshift 1 < z < 3 from the LUCIFER instrument on the Large Binocular Telescope and the Infrared Spectrograph on Spitzer. The sample was selected to represent pure, actively star-forming systems, absent of active galactic nuclei. The large lensing magnifications result in high signal-to-noise spectra that can probe faint IR recombination lines, including Pa-alpha and Br-alpha at high redshifts. The sample was augmented by three lensed galaxies with similar suites of unpublished data and observations from the literature, resulting in the final sample of seven galaxies. We use the IR recombination lines in conjunction with H-alpha observations to probe the extinction, Av, of these systems, as well as testing star formation rate (SFR) indicators against the SFR measured by fitting spectral energy distributions to far-IR photometry. Our galaxies occupy a range of Av from ~0 to 5.9 mag, larger than previously known for a similar range of IR luminosities at these redshifts. Thus, estimates of SFR even at z ~ 2 must take careful count of extinction in the most IR luminous galaxies. We also measure extinction by comparing SFR estimates from optical emission lines with those from far-IR measurements. The comparison of results from these two independent methods indicates a large variety of dust distribution scenarios at 1 < z < 3. Without correcting for dust extinction, the H-alpha SFR indicator underestimates the SFR; the size of the necessary correction depends on the IR luminosity and dust distribution scenario. Individual SFR estimates based on the 6.2 micron PAH emission line luminosity do not show a systematic discrepancy with extinction, although a considerable, ~0.2 dex scatter is observed.Comment: Accepted for publication in The Astrophysical Journal; 14 pages, 8 figure