Imaging the Molecular Gas in A z=3.9 Quasar Host Galaxy at 0\farcs3 Resolution: A Central, Sub-Kilparsex Scale Star Formation Reservoir in APM 08279+5255

We have mapped the molecular gas content in the host galaxy of the strongly lensed high-redshift quasar APM 08279+5255 (z = 3.911) with the Very Large Array at 0\farcs3 resolution. The CO(J = 1➝0) emission is clearly resolved in our maps. The CO(J = 1➝0) line luminosity derived from these maps is in good agreement with a previous single-dish measurement. In contrast to previous interferometer-based studies, we find that the full molecular gas reservoir is situated in two compact peaks separated by ≲0\farcs4. Our observations reveal, for the first time, that the emission from cold molecular gas is virtually co-spatial with the optical/near-infrared continuum emission of the central active galactic nucleus (AGN) in this source. This striking similarity in morphology indicates that the molecular gas is situated in a compact region close to the AGN. Based on the high-resolution CO maps, we present a revised model for the gravitational lensing in this system, which indicates that the molecular gas emission is magnified by only a factor of 4 (in contrast to previously suggested factors of 100). This model suggests that the CO is situated in a circumnuclear disk of ~550 pc radius that is possibly seen at an inclination of ≲25°, i.e., relatively close to face-on. From the CO luminosity, we derive a molecular gas mass of Mgas = 1.3x10^11 M☉ for this galaxy. From the CO structure and linewidth, we derive a dynamical mass of M dyn sin^2 i = 4.0x10^10 M☉. Based on a revised mass estimate for the central black hole of Mbh = 2.3x10^10 M☉ and the results of our molecular line study, we find that the mass of the stellar bulge of APM 08279+5255 falls short of the local M BH-σbulge relationship of nearby galaxies by more than an order of magnitude, lending support to recent suggestions that this relation may evolve with cosmic time and/or change toward the high-mass end

Extended Cold Molecular Gas Reservoirs in z~3.4 Submillimeter Galaxies

We report the detection of spatially resolved CO(1-0) emission in the z~3.4 submillimeter galaxies (SMGs) SMM J09431+4700 and SMM J13120+4242, using the Expanded Very Large Array (EVLA). SMM J09431+4700 is resolved into the two previously reported millimeter sources H6 and H7, separated by ~30kpc in projection. We derive CO(1-0) line luminosities of L'(CO 1-0) = (2.49+/-0.86) and (5.82+/-1.22) x 10^10 K km/s pc^2 for H6 and H7, and L'(CO 1-0) = (23.4+/-4.1) x 10^10 K km/s pc^2 for SMM J13120+4242. These are ~1.5-4.5x higher than what is expected from simple excitation modeling of higher-J CO lines, suggesting the presence of copious amounts of low-excitation gas. This is supported by the finding that the CO(1-0) line in SMM J13120+4242, the system with lowest CO excitation, appears to have a broader profile and more extended spatial structure than seen in higher-J CO lines (which is less prominently seen in SMM J09431+4700). Based on L'(CO 1-0) and excitation modeling, we find M_gas = 2.0-4.3 and 4.7-12.7 x 10^10 Msun for H6 and H7, and M_gas = 18.7-69.4 x 10^10 Msun for SMM J13120+4242. The observed CO(1-0) properties are consistent with the picture that SMM J09431+4700 represents an early-stage, gas-rich major merger, and that SMM J13120+4242 represents such a system in an advanced stage. This study thus highlights the importance of spatially and dynamically resolved CO(1-0) observations of SMGs to further understand the gas physics that drive star formation in these distant galaxies, which becomes possible only now that the EVLA rises to its full capabilities.Comment: 6 pages, 4 figures, to appear in ApJL (EVLA Special Issue; accepted May 19, 2011

Sensitive VLBI Continuum and H I Absorption Observations of NGC 7674: First Scientific Observations with the Combined Array VLBA, VLA & Arecibo

We present phase-referenced VLBI observations of the radio continuum emission from, and the H I 21 cm absorption toward, the Luminous Infrared Galaxy NGC 7674. The observations were carried out at 1380 MHz using the VLBA, the phased VLA, and theArecibo radio telescope. These observations constitute the first scientific use of the Arecibo telescope in a VLBI observation with the VLBA. The high- and low-resolution radio continuum images reveal several new continuum structures in the nuclear region of this galaxy. At ~100 mas resolution, we distinguish six continuum structures extending over 1.4 arcsec, with a total flux density of 138 mJy. Only three of these structures were known previously. All these structures seem to be related to AGN activity. At the full resolution of the array, we only detect two of the six continuum structures. Both are composed of several compact components with brightness temperatures on the order of $10^{7}$ K. While it is possible that one of these compact structures could host an AGN, they could also be shock-like features formed by the interaction of the jet with compact interstellar clouds in the nuclear region of this galaxy. Complex H I absorption is detected with our VLBI array at both high and low angular resolution. Assuming that the widest H I feature is associated with a rotating H I disk or torus feeding a central AGN, we estimate an enclosed dynamical mass of ~7 x 10^7 M_sun, comparable to the value derived from the hidden broad H$\beta$ emission in this galaxy. The narrower H I lines could represent clumpy neutral hydrogen structures in the H I torus. The detection of H I absorption toward some of the continuum components, and its absence toward others, suggest an inclined H I disk or torus in the central region of NGC 7674.Comment: 37 pages, 11 figures. ApJ accepted. To appear in the Nov. 10, 2003 issue of ApJ. Please use the PDF version if the postscript doesn't show the figure

Observations of Dense Molecular Gas in a Quasar Host Galaxy at z=6.42: Further Evidence for a Non-Linear Dense Gas - Star Formation Relation at Early Cosmic Times

We report a sensitive search for the HCN(J=2-1) emission line towards SDSS J1148+5251 at z=6.42 with the VLA. HCN emission is a star formation indicator, tracing dense molecular hydrogen gas (n(H2) >= 10^4 cm^-3) within star-forming molecular clouds. No emission was detected in the deep interferometer maps of J1148+5251. We derive a limit for the HCN line luminosity of L'(HCN) < 3.3 x 10^9 K km/s pc^2, corresponding to a HCN/CO luminosity ratio of L'(HCN)/L'(CO) < 0.13. This limit is consistent with a fraction of dense molecular gas in J1148+5251 within the range of nearby ultraluminous infrared galaxies (ULIRGs; median value: L'(HCN)/L'(CO) = 0.17 {+0.05/-0.08}) and HCN-detected z>2 galaxies (0.17 {+0.09/-0.08}). The relationship between L'(HCN) and L(FIR) is considered to be a measure for the efficiency at which stars form out of dense gas. In the nearby universe, these quantities show a linear correlation, and thus, a practically constant average ratio. In J1148+5251, we find L(FIR)/L'(HCN) > 6600. This is significantly higher than the average ratios for normal nearby spiral galaxies (L(FIR)/L'(HCN) = 580 {+510/-270}) and ULIRGs (740 {+505/-50}), but consistent with a rising trend as indicated by other z>2 galaxies (predominantly quasars; 1525 {+1300/-475}). It is unlikely that this rising trend can be accounted for by a contribution of AGN heating to L(FIR) alone, and may hint at a higher median gas density and/or elevated star-formation efficiency toward the more luminous high-redshift systems. There is marginal evidence that the L(FIR)/L'(HCN) ratio in J1148+5251 may even exceed the rising trend set by other z>2 galaxies; however, only future facilities with very large collecting areas such as the SKA will offer the sensitivity required to further investigate this question.Comment: 5 pages, 2 figures, 2 tables, to appear in ApJL (accepted October 24, 2007

The molecular gas content of z > 6.5 Lyman-alpha emitters

We present results from a sensitive search for CO J=1-0 line emission in two z> 6.5 Lyman-alpha emitters (LAEs) with the Green Bank Telescope. CO J=1-0 emission was not detected from either object. For HCM 6A, at z ~ 6.56, the lensing magnification factor of ~4.5 implies that the CO non-detection yields stringent constraints on the CO J=1-0 line luminosity and molecular gas mass of the LAE, L'(CO) < 6.1x10^9 x (dV/300)^(1/2) K km/s pc^2 and M(H_2) < 4.9x10^9 x (dV/300)^(1/2) x (X(CO)/0.8) Msun. These are the strongest limits obtained so far for a z >~ 6 galaxy. For IOK-1, the constraints are somewhat less sensitive, L'(CO) < 2.3x10^10 x (dV/300)^(1/2) K km/s pc^2 and M(H_2) < 1.9x10^10 x (dV/300)^(1/2) x (X(CO)/0.8) Msun. The non-detection of CO J=1-0 emission in HCM~6A, whose high estimated star formation rate, dust extinction, and lensing magnification make it one of the best high-z LAEs for such a search, implies that typical z >~ 6 LAEs are likely to have significantly lower CO line luminosities than massive sub-mm galaxies and hyperluminous infrared quasars at similar redshifts, due to either a significantly lower molecular gas content or a higher CO-to-H_2 conversion factor.Comment: Accepted for publication in ApJ Letter

High Sensitivity Array Observations of the z=4.4z = 4.4 QSO BRI 1335-0417

We present sensitive phase-referenced VLBI results on the radio continuum emission from the $z=4.4$ QSO BRI 1335--0417. The observations were carried out at 1.4 GHz using the High Sensitivity Array (HSA). Our sensitive VLBI image at $189 \times 113$ mas ($1.25 \times 0.75$ kpc) resolution shows continuum emission in BRI 1335--0417 with a total flux density of $208 \pm 46 \mu$Jy, consistent with the flux density measured with the VLA. The size of the source at FWHM is $255 \times 138$ mas ($1.7 \times 0.9$ kpc) and the derived intrinsic brightness temperature is $\sim 3.5\times 10^4$ K. No continuum emission is detected at the full VLBI resolution ($32 \times 7$ mas, $211 \times 46$ pc), with a 4$\sigma$ point source upper limit of 34 $\mu$Jy beam$^{-1}$, or an upper limit to the intrinsic brightness temperature of $5.6\times 10^5$ K. The highest angular resolution with at least a 4.5$\sigma$ detection of the radio continuum emission is $53 \times 27$ mas ($0.35 \times 0.18$ kpc). At this resolution, the image shows a continuum feature in BRI 1335--0417 with a size of $64 \times 35$ mas ($0.42 \times 0.23$ kpc) at FWHM, and intrinsic brightness temperature of $\sim 2\times 10^5$ K. The extent of the observed continuum sources at 1.4 GHz and the derived brightness temperatures show that the radio emission (and thus presumably the far-infrared emission) in BRI 1335--0417 is powered by a major starburst, with a massive star formation rate of order a few thousand M_{\odot} {\rm yr}^{-1}$. Moreover, the absence of any compact high-brightness temperature source suggests that there is no radio-loud AGN in this$z=4.4$ QSO.Comment: 13 pages, 3 figures, AJ accepte

Formation of a Quasar Host Galaxy through a Wet Merger 1.4 Billion Years after the Big Bang

We present high-resolution Very Large Array imaging of the molecular gas in the host galaxy of the high redshift quasar BRI 1335-0417 (z=4.41). Our CO(2-1) observations have a linear resolution of 0.15" (1.0 kpc) and resolve the molecular gas emission both spatially and in velocity. The molecular gas in BRI 1335-0417 is extended on scales of 5 kpc, and shows a complex structure. At least three distinct components encompassing about two thirds of the total molecular mass of 9.2 x 10^10 M_sun are identified in velocity space, which are embedded in a structure that harbors about one third of the total molecular mass in the system. The brightest CO(2-1) line emission region has a peak brightness temperature of 61+/-9 K within 1 kpc diameter, which is comparable to the kinetic gas temperature as predicted from the CO line excitation. This is also comparable to the gas temperatures found in the central regions of nearby ultra-luminous infrared galaxies, which are however much more compact than 1 kpc. The spatial and velocity structure of the molecular reservoir in BRI 1335-0417 is inconsistent with a simple gravitationally bound disk, but resembles a merging system. Our observations are consistent with a major, gas-rich (`wet') merger that both feeds an accreting supermassive black hole (causing the bright quasar activity), and fuels a massive starburst that builds up the stellar bulge in this galaxy. Our study of this z>4 quasar host galaxy may thus be the most direct observational evidence that `wet' mergers at high redshift are related to AGN activity.Comment: 5 pages, 4 figures, to appear in ApJL (accepted August 27, 2008