Mystery of the Lyα Blobs

We present Spitzer Space Telescope observations of the extended Lyman α blobs associated with the z=2.38 over-density J2143-4423, the largest known structure (110 Mpc) above z=2. We detect all 4 of the Lyα blobs in all four IRAC channels and we also detect 3 out of 4 of the blobs with MIPS 24μm. Conversion from rest-wavelength 7μm to total far-infrared luminosity using locally derived correlations suggests all the detected sources are in the class of ULIRGs or even Hyper-LIRGs. We find a weak correlation between Lyα and mid-infrared emission for the Lyα blobs (L_(Lyα)/L_(bol) = 0.05-0.2%). Nearly all Lyα blobs show some evidence for interaction, either in HST imaging, or the proximity of multiple MIPS sources within the Lyα cloud. This suggests that interaction or even mergers may be related to the production of Lyα blobs. Optical through infrared SEDs of the Lyα blobs do not show a clear 1.6μm bump, but rather are indicative of a composite of star formation and AGN energy sources

Ultraviolet-Bright, High-Redshift ULIRGS

We present Spitzer Space Telescope observations of the z=2.38 lya-emitter over-density associated with galaxy cluster J2143-4423, the largest known structure (110 Mpc) above z=2. We imaged 22 of the 37 known lya-emitters within the filament-like structure, using the MIPS 24um band. We detected 6 of the lya-emitters, including 3 of the 4 clouds of extended (>50 kpc) lyman alpha emission, also known as Lya Blobs. Conversion from rest-wavelength 7um to total far-infrared luminosity using locally derived correlations suggests all the detected sources are in the class of ULIRGs, with some reaching Hyper-LIRG energies. Lya blobs frequently show evidence for interaction, either in HST imaging, or the proximity of multiple MIPS sources within the Lya cloud. This connection suggests that interaction or even mergers may be related to the production of Lya blobs. A connection to mergers does not in itself help explain the origin of the Lya blobs, as most of the suggested mechanisms for creating Lya blobs (starbursts, AGN, cooling flows) could also be associated with galaxy interactions.Comment: 12 pages, 3 figures, accepted by ApJ Letter

PAH Emission Within Lyman Alpha Blobs

We present Spitzer observations of Lya Blobs (LAB) at z=2.38-3.09. The mid-infrared ratios (4.5/8um and 8/24um) indicate that ~60% of LAB infrared counterparts are cool, consistent with their infrared output being dominated by star formation and not active galactic nuclei (AGN). The rest have a substantial hot dust component that one would expect from an AGN or an extreme starburst. Comparing the mid-infrared to submillimeter fluxes (~850um or rest frame far infrared) also indicates a large percentage (~2/3) of the LAB counterparts have total bolometric energy output dominated by star formation, although the number of sources with sub-mm detections or meaningful upper limits remains small (~10). We obtained Infrared Spectrograph (IRS) spectra of 6 infrared-bright sources associated with LABs. Four of these sources have measurable polycyclic aromatic hydrocarbon (PAH) emission features, indicative of significant star formation, while the remaining two show a featureless continuum, indicative of infrared energy output completely dominated by an AGN. Two of the counterparts with PAHs are mixed sources, with PAH line-to-continuum ratios and PAH equivalent widths indicative of large energy contributions from both star formation and AGN. Most of the LAB infrared counterparts have large stellar masses, around 10^11 Mo. There is a weak trend of mass upper limit with the Lya luminosity of the host blob, particularly after the most likely AGN contaminants are removed. The range in likely energy sources for the LABs found in this and previous studies suggests that there is no single source of power that is producing all the known LABs.Comment: 34 pages, 5 figures, accepted by Ap

Polycyclic Aromatic Hydrocarbon Emission within Lyα Blobs

We present Spitzer observations of Lyα blobs (LABs) at z = 2.38-3.09. The mid-infrared ratios (4.5 μm/8 μm and 8 μm/24 μm) indicate that ~60% of LAB infrared counterparts are cool, consistent with their infrared output being dominated by star formation and not active galactic nuclei (AGNs). The rest have a substantial hot dust component that one would expect from an AGN or an extreme starburst. Comparing the mid-infrared to submillimeter fluxes (~850 μm or rest-frame far-infrared) also indicates that a large percentage (~2/3) of the LAB counterparts have total bolometric energy output dominated by star formation, although the number of sources with submillimeter detections or meaningful upper limits remains small (~10). We obtained Infrared Spectrograph (IRS) spectra of six infrared-bright sources associated with LABs. Four of these sources have measurable polycyclic aromatic hydrocarbon (PAH) emission features, indicative of significant star formation, while the remaining two show a featureless continuum, indicative of infrared energy output completely dominated by an AGN. Two of the counterparts with PAHs are mixed sources, with PAH line-to-continuum ratios and PAH equivalent widths indicative of large energy contributions from both star formation and AGN. Most of the LAB infrared counterparts have large stellar masses, around 10^(11) M_⊙. There is a weak trend of mass upper limit with the Lyα luminosity of the host blob, particularly after the most likely AGN contaminants are removed. The range in likely energy sources for the LABs found in this and previous studies suggests that there is no single source of power that is producing all the known LABs

A Deep ROSAT HRI Observation of NGC 1313

We describe a series of observations of NGC 1313 using the ROSAT HRI with a combined exposure time of 183.5 ksec. The observations span an interval between 1992 and 1998; the purpose of observations since 1994 was to monitor the X-ray flux of SN1978K, one of several luminous sources in the galaxy. No diffuse emission is detected in the galaxy to a level of ~1-2x10^37 ergs/s/arcmin^-2. A total of eight sources are detected in the summed image within the D_25 diameter of the galaxy. The luminosities of five of the eight range from \~6x10^37 to ~6x10^38 erg/s; these sources are most likely accreting X-ray binaries, similar to sources obseved in M31 and M33. The remaining three sources all emit above 10^39 erg/s. We present light curves of the five brightest sources. Variability is detected at the 99.9% level from four of these. We identify one of the sources as an NGC 1313 counterpart of a Galactic X-ray source. The light curve, though crudely sampled, most closely resembles that of a Galactic black hole candidate such as GX339-4, but with considerably higher peak X-ray luminosity. An additional seven sources lie outside of the D_25 diameter and are either foreground stars or background AGN.Comment: 18 pages, 9 figures; accepted AJ, scheduled for November 200

Rotating black hole orbit functionals in the frequency domain

In many astrophysical problems, it is important to understand the behavior of functions that come from rotating (Kerr) black hole orbits. It can be particularly useful to work with the frequency domain representation of those functions, in order to bring out their harmonic dependence upon the fundamental orbital frequencies of Kerr black holes. Although, as has recently been shown by W. Schmidt, such a frequency domain representation must exist, the coupled nature of a black hole orbit's $r$ and $\theta$ motions makes it difficult to construct such a representation in practice. Combining Schmidt's description with a clever choice of timelike coordinate suggested by Y. Mino, we have developed a simple procedure that sidesteps this difficulty. One first Fourier expands all quantities using Mino's time coordinate $\lambda$. In particular, the observer's time $t$ is decomposed with $\lambda$. The frequency domain description is then built from the $\lambda$-Fourier expansion and the expansion of $t$. We have found this procedure to be quite simple to implement, and to be applicable to a wide class of functionals. We test the procedure using a simple test function, and then apply it in a particularly interesting case, the Weyl curvature scalar $\psi_4$ used in black hole perturbation theory.Comment: 16 pages, 2 figures. Submitted to Phys Rev D. New version gives a vastly improved algorithm due to Drasco for computing the Fourier transforms. Drasco has been added as an author. Also fixed some references and exterminated a small herd of typos; final published versio

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

NICMOS Snapshot Survey of Damped Lyman Alpha Quasars

We image 19 quasars with 22 damped Lyman alpha (DLA) systems using the F160W filter and the Near-Infrared Camera and Multiobject Spectrograph aboard the Hubble Space Telescope, in both direct and coronagraphic modes. We reach 5 sigma detection limits of ~H=22 in the majority of our images. We compare our observations to the observed Lyman-break population of high-redshift galaxies, as well as Bruzual & Charlot evolutionary models of present-day galaxies redshifted to the distances of the absorption systems. We predict H magnitudes for our DLAs, assuming they are producing stars like an L* Lyman-break galaxy (LBG) at their redshift. Comparing these predictions to our sensitivity, we find that we should be able to detect a galaxy around 0.5-1.0 L* (LBG) for most of our observations. We find only one new possible candidate, that near LBQS0010-0012. This scarcity of candidates leads us to the conclusion that most DLA systems are not drawn from a normal LBG luminosity function nor a local galaxy luminosity function placed at these high redshifts.Comment: 31 pages, 8 figures, Accepted for Feb. 10 issue of Ap