arXiv subjects

Jeff Wagg

Publications and source records attributed to Jeff Wagg.

At least 73 records · Page 4Linked to original sources

arXiv2013

Star Formation and Gas Kinematics of Quasar Host Galaxies at z~6: New insights from ALMA

We present ALMA observations of the [C II] 158 micron fine structure line and dust continuum emission from the host galaxies of five redshift 6 quasars. We also report complementary observations of 250 GHz dust continuum and CO (6-5) line emission from the z=6.00 quasar SDSS J231038.88+185519.7. The ALMA observations were carried out in the extended array at 0.7" resolution. We have detected the line and dust continuum in all five objects. The derived [C II] line luminosities are 1.6x10^{9} to 8.8x10^{9} Lsun and the [C II]-to-FIR luminosity ratios are 3.0-5.6x10^{-4}, which is comparable to the values found in other high-redshift quasar-starburst systems and local ultra-luminous infrared galaxies. The sources are marginally resolved and the intrinsic source sizes (major axis FWHM) are constrained to be 0.3" to 0.6" (i.e., 1.7 to 3.5 kpc) for the [C II] line emission and 0.2" to 0.4" (i.e., 1.2 to 2.3 kpc) for the continuum. These measurements indicate that there is vigorous star formation over the central few kpc in the quasar host galaxies. The ALMA observations also constrain the dynamical properties of the atomic gas in the starburst nuclei. The intensity-weighted velocity maps of three sources show clear velocity gradients. Such velocity gradients are consistent with a rotating, gravitationally bound gas component, although they are not uniquely interpreted as such. Under the simplifying assumption of rotation, the implied dynamical masses within the [C II]-emitting regions are of order 10^{10} to 10^{11} Msun. Given these estimates, the mass ratios between the SMBHs and the spheroidal bulge are an order of magnitude higher than the mean value found in local spheroidal galaxies, which is in agreement with results from previous CO observations of high redshift quasars.

astro-ph.CO↗

arXiv2013

Probing the Interstellar Medium of z~1 Ultra-luminous Infrared Galaxies through Interferometric Observations of CO and Spitzer Mid-infrared Spectroscopy

We explore the relationship between gas, dust and star formation in a sample of 12 ultra-luminous infrared galaxies (ULIRGs) at high redshift compared to a similar sample of local galaxies. We present new CO observations and/or Spitzer mid-IR spectroscopy for 6 70 micron selected galaxies at z~1 in order to quantify the properties of the molecular gas reservoir, the contribution of an active galactic nuclei (AGN) to the mid-IR luminosity and the star formation efficiency (SFE=LIR/L'CO). The mid-IR spectra show strong polycyclic aromatic hydrocarbon (PAH) emission and our spectral decomposition suggests that the AGN makes a minimal contribution (<25%) to the mid-IR luminosity. The 70 micron selected ULIRGs which we find to be spectroscopic close pairs, are observed to have high SFE, similar to local ULIRGs and high redshift submillimeter galaxies, consistent with enhanced IR luminosity due to an ongoing major merger. Combined with existing observations of local and high redshift ULIRGs, we further compare the PAH, IR and CO luminosities. We show that the ratio LPAH6.2/LIR decreases with increasing IR luminosity for both local and high redshift galaxies but the trend for high redshift galaxies is shifted to higher IR luminosities; the average LPAH6.2/LIR ratio at a given LIR is ~3 times higher at high redshift. When we normalize by the molecular gas, we find this trend to be uniform for galaxies at all redshifts and that the molecular gas is correlated with the PAH dust emission.The similar trends seen in the [CII] to molecular gas ratios in other studies suggests that PAH emission, like [CII], continues to be a good tracer of photodissociation regions even at high redshift. Together the CO, PAH and far-IR fine structure lines should be useful for constraining the interstellar medium conditions in high redshift galaxies.

astro-ph.CO↗

arXiv2013

A search for CII-158$μ$m line emission in HCM\,6A, a Lyman-$α$ emitter at $z=6.56$

We report a Plateau de Bure interferometer search for CII-158$μ$m emission from HCM6A, a lensed Lyman-$α$ emitter (LAE) at $z = 6.56$. Our non-detections of CII-158$μ$m line emission and 1.2mm radio continuum emission yield $3σ$ limits of L$_{\rm CII} < 6.4 \times 10^7 \times (ΔV/100 km s^{-1})^{1/2}$ L$_\odot$ on the CII-158$μ$m line luminosity and S$_{\rm 1.2mm} < 0.68$ mJy on the 1.2mm flux density. The local conversion factor between L$_{\rm CII}$ and star formation rate (SFR) yields an SFR $< 4.7$ M$_\odot$ yr$^{-1}$, $\approx 2$ times lower than that inferred from the ultraviolet (UV) continuum, suggesting that the local factor may not be applicable in high-$z$ LAEs. The non-detection of 1.2mm continuum emission yields a total SFR $< 28$ M$_\odot$/yr; any obscured star formation is thus within a factor of two of the visible star formation. Our best-fit model to the rest-frame UV/optical spectral energy distribution of HCM6A yields a stellar mass of $1.3 \times 10^9$ M$_\odot$ and an SFR of ~10 M$_\odot$/yr, with negligible dust obscuration. We fortuitously detect CO J=3-2 emission from a $z=0.375$ galaxy in the foreground cluster Abell370, obtaining a CO line luminosity of L$^\prime ({\rm CO}) > (8.95 \pm 0.79) \times 10^8$ K km s$^{-1}$ pc$^2$, and a molecular gas mass of M$({\rm H_2}) > (4.12 \pm 0.36) \times 10^9$ M$_\odot$, for a CO-to-H$_2$ conversion factor of 4.6 M$_\odot$ (K km s$^{-1}$ pc$^2$)$^{-1}$.

astro-ph.CO↗

arXiv2012

Star Formation in Quasar Host Galaxies at Redshift 6: Millimeter Surveys and New Insights from ALMA

We have been carrying out a systematic survey of the star formation and ISM properties in the host galaxies of z~6 quasars. Our 250 GHz observations, together with available data from the literature, yield a sample of 14 z~6 quasars that are bright in millimeter dust continuum emission with estimated FIR luminosities of a few 10^12 to 10^13 Lsun. Most of these millimeter-detected z~6 quasars have also been detected in molecular CO line emission, indicating molecular gas masses on order of 10^10 Msun. We have searched for [C II] 158 micron fine structure line emission toward four of the millimeter bright z~6 quasars with ALMA and all of them have been detected. All these results suggest massive star formation at rates of about 600 to 2000 Msun/yr over the central few kpc region of these quasar host galaxies.

astro-ph.CO↗

arXiv2012

A deep search for CO J=2-1 emission from a Lyman-Alpha blob at z~6.595

We have used the Green Bank Telescope to carry out a deep search for redshifted CO J=2-1 line emission from an extended (>17 kpc) Ly-Alpha blob (LAB), "Himiko", at z~6.595. Our non-detection of CO J=2-1 emission places the strong 3-sigma upper limit of L'_CO < 1.8x10^10 x sqrt(dV/250) K km/s pc^2 on the CO line luminosity. This is comparable to the best current limits on the CO line luminosity in LABs at z~3 and lower-luminosity Lyman-Alpha emitters (LAEs) at z>~6.5. High-z LABs appear to have lower CO line luminosities than the host galaxies of luminous quasars and sub-mm galaxies at similar redshifts, despite their high stellar mass. Although the CO-to-H2 conversion factor is uncertain for galaxies in the early Universe, we assume X_CO = 0.8 Msun (K km/s pc^2)^-1 to obtain the limit M(H_2) < 1.4 x 10^10 Msun on Himiko's molecular gas mass; this is a factor of >2.5 lower than the stellar mass in the z~6.595 LAB.

astro-ph.CO↗

arXiv2012

CO J=2-1 line emission in cluster galaxies at z~1: fueling star formation in dense environments

We present observations of CO J=2-1 line emission in infrared-luminous cluster galaxies at z~1 using the IRAM Plateau de Bure Interferometer. Our two primary targets are optically faint, dust-obscured galaxies (DOGs) found to lie within 2 Mpc of the centers of two massive (>10^14 Msun) galaxy clusters. CO line emission is not detected in either DOG. We calculate 3-sigma upper limits to the CO J=2-1 line luminosities, L'_CO < 6.08x10^9 and < 6.63x10^9 K km/s pc^2. Assuming a CO-to-H_2 conversion factor derived for ultraluminous infrared galaxies in the local Universe, this translates to limits on the cold molecular gas mass of M_H_2 < 4.86x10^9 Msun and M_H_2 < 5.30x10^9 Msun. Both DOGs exhibit mid-infrared continuum emission that follows a power-law, suggesting that an AGN contributes to the dust heating. As such, estimates of the star formation efficiencies in these DOGs are uncertain. A third cluster member with an infrared luminosity, L_IR < 7.4x10^11 Lsun, is serendipitously detected in CO J=2-1 line emission in the field of one of the DOGs located roughly two virial radii away from the cluster center. The optical spectrum of this object suggests that it is likely an obscured AGN, and the measured CO line luminosity is L'_CO = (1.94 +/- 0.35)x10^10 K km/s pc^2, which leads to an estimated cold molecular gas mass M_H_2 = (1.55+/-0.28)x10^10 Msun. A significant reservoir of molecular gas in a z~1 galaxy located away from the cluster center demonstrates that the fuel can exist to drive an increase in star-formation and AGN activity at the outskirts of high-redshift clusters.

astro-ph.CO↗

arXiv2011

Far-infrared and Molecular CO Emission From the Host Galaxies of Faint Quasars at z~6

We present new millimeter and radio observations of nine z~6 quasars discovered in deep optical and near-infrared surveys. We observed the 250 GHz continuum in eight of the nine objects and detected three of them. New 1.4 GHz radio continuum data have been obtained for four sources, and one has been detected. We searched for molecular CO (6-5) line emission in the three 250 GHz detections and detected two of them. We study the FIR and radio emission and quasar-host galaxy evolution with a sample of 18 z~6 quasars that are faint at UV/optical wavelengths (rest-frame 1450A magnitudes of m_1450\ge20.2). The average FIR-to-AGN UV luminosity ratio of this faint quasar sample is about two times higher than that of the bright quasars at z~6 (m_1450<20.2). A fit to the average FIR and AGN bolometric luminosities of both the UV/optically faint and bright z~6 quasars, and the average luminosities of samples of submillimeter /millimeter-observed quasars at z~2 to 5, yields a relationship of L_{FIR} {L_{bol}}^{0.62}. Five of the 18 faint z~6 quasars have been detected at 250 GHz. These 250 GHz detections, as well as most of the millimeter-detected optically bright z~6 quasars, follow a shallower trend of L_{FIR} {L_{bol}}^{0.45} defined by the starburst-AGN systems in local and high-z universe. The millimeter continuum detections in the five objects and molecular CO detections in three of them reveal a few x10^8 M_sun of FIR-emitting warm dust and 10^10 M_sun of molecular gas in the quasar host galaxies. All these results argue for massive star formation in the quasar host galaxies, with estimated star formation rates of a few hundred M_sun yr^{-1}. Additionally, the higher FIR-to-AGN luminosity ratio found in these 250 GHz-detected faint quasars also suggests a higher ratio between star formation rate and supermassive black hole accretion rate than the UV/optically most luminous quasars at z~6.

astro-ph.CO↗

arXiv2011

CO(1-0) in z>2 Quasar Host Galaxies: No Evidence for Extended Molecular Gas Reservoirs

We report the detection of CO(1-0) emission in the strongly lensed high-redshift quasars IRAS F10214+4724 (z=2.286), the Cloverleaf (z=2.558), RX J0911+0551 (z=2.796), SMM J04135+10277 (z=2.846), and MG 0751+2716 (z=3.200), using the Expanded Very Large Array and the Green Bank Telescope. We report lensing-corrected CO(1-0) line luminosities of L'(CO) = 0.34-18.4 x 10^10 K km/s pc^2 and total molecular gas masses of M(H2) = 0.27-14.7 x 10^10 Msun for the sources in our sample. Based on CO line ratios relative to previously reported observations in J>=3 rotational transitions and line excitation modeling, we find that the CO(1-0) line strengths in our targets are consistent with single, highly-excited gas components with constant brightness temperature up to mid-J levels. We thus do not find any evidence for luminous extended, low excitation, low surface brightness molecular gas components. These properties are comparable to those found in z>4 quasars with existing CO(1-0) observations. These findings stand in contrast to recent CO(1-0) observations of z~2-4 submillimeter galaxies (SMGs), which have lower CO excitation and show evidence for multiple excitation components, including some low-excitation gas. These findings are consistent with the picture that gas-rich quasars and SMGs represent different stages in the early evolution of massive galaxies.

astro-ph.CO↗

arXiv2011

Unveiling the mask on the ULIRG-to-QSO transition object [H89]1821+643 at z=0.3: a gas-poor/gas-rich galaxy merger and the implications for CO-based dynamical mass estimates

We report the detection of the CO J=1-0 emission line in [H89]1821+643, one of the most optically luminous QSOs in the local Universe and a template ULIRG-to-QSO transition object, located in a rich cool-core cluster at z=0.297. The CO emission is likely to be extended, highly asymmetric with respect to the center of the host elliptical where the QSO resides, and corresponds to a molecular gas mass of ~ 8.0 x 10^{9} M_sun. The dynamical mass enclosed by the CO line emission region could amount up to ~ 1.7x10^{12} M_sun (80% of the total mass of the elliptical host). The bulk of the CO emission is located at ~9 kpc south-east from the nuclei position, and close to a faint optical structure, suggesting that the CO emission could either represent a gas-rich companion galaxy merging with the elliptical host or a tail-like structure reminiscent of a previous interaction. We argue that the first scenario is more likely given the large masses implied for the CO source, which would imply a highly asymmetrical elliptical host. The close alignment between the CO emission major axis and the radio-plume suggests a possible role of the latter excitation of the ambient gas reservoir. The stacking technique was used to search for CO emission and 3mm continuum emission from galaxies in the surrounding cluster, however no detection was found either toward individual galaxies or the stacked ensemble of galaxies, with a 3 sigma limit of < 1.1x10^9 M_sun for the molecular gas.

astro-ph.CO↗

arXiv2011

CO (2-1) Line Emission in Redshift 6 Quasar Host Galaxies

We report new observations of CO (2-1) line emission toward five z~6 quasars using the Ka-band receiver system on the Expanded Very Large Array (EVLA). Strong detections were obtained in two of them, SDSS J092721.82+200123.7 and CFHQS J142952.17+544717.6, and a marginal detection was obtained in another source, SDSS J084035.09+562419.9. Upper limits of the CO (2-1) line emission have been obtained for the other two objects. The CO (2-1) line detection in J0927+2001, together with previous measurements of the CO (6-5) and (5-4) lines, reveals important constraints on the CO excitation in the central ~10 kpc region of the quasar host galaxy. The CO (2-1) line emission from J1429+5447 is resolved into two distinct peaks separated by 1.2" (~6.9 kpc), indicating a possible gas-rich, major merging system, and the optical quasar position is consistent with the west peak. This result is in good agreement with the picture in which intense host galaxy star formation is coeval with rapid supermassive black hole accretion in the most distant universe. The two EVLA detections are ideal targets for further high-resolution imaging (e.g., with ALMA or EVLA observations) to study the gas distribution, dynamics, and SMBH-bulge mass relation in these earliest quasar-host galaxy systems.

astro-ph.CO↗

arXiv2011

Imaging the Molecular Gas Properties of a Major Merger Driving the Evolution of a z=2.5 Submillimeter Galaxy

We report the detection of spatially extended CO 1-0 and 5-4 emission in the z=2.49 submillimeter galaxy (SMG) J123707+6214, using the Expanded Very Large Array and the Plateau de Bure Interferometer. The large molecular gas reservoir is spatially resolved into two CO(1-0) components (north-east and south-west; previously identified in CO 3-2 emission) with gas masses of 4.3 and 3.5 x 10^10 (alpha_CO/0.8) Msun. We thus find that the optically invisible north-east component slightly dominates the gas mass in this system. The total molecular gas mass derived from the CO(1-0) observations is ~2.5 times larger than estimated from CO(3-2). The two components are at approximately the same redshift, but separated by ~20 kpc in projection. The morphology is consistent with that of an early-stage merger. The total amount of molecular gas is sufficient to maintain the intense 500 Msun/yr starburst in this system for at least ~160 Myr. We derive line brightness temperature ratios of r_31=0.39+/-0.09 and 0.37+/-0.10, and r_51=0.26+/-0.07 and 0.25+/-0.08 in the two components, respectively, suggesting that the J>=3 lines are substantially subthermally excited. This also suggests comparable conditions for star formation in both components. Given the similar gas masses of both components, this is consistent with the comparable starburst strengths observed in the radio continuum emission. Our findings are consistent with other recent studies that find evidence for lower CO excitation in SMGs than in high-z quasar host galaxies with comparable gas masses. This may provide supporting evidence that both populations correspond to different evolutionary stages in the formation of massive galaxies.

astro-ph.CO↗

arXiv2010

Dense Molecular Gas Excitation in Nuclear Starbursts at High Redshift: HCN, HNC, and HCO+(J=6-5) Emission in the z=3.91 Quasar Host of APM08279+5255

We report the detection of surprisingly strong HCN, HNC, and HCO+(J=6-5) emission in the host galaxy of the z=3.91 quasar APM08279+5255 through observations with CARMA. HCN, HNC, and HCO+ are typically used as star formation indicators, tracing dense molecular hydrogen gas [n(H2) > 10^5,cm^-3] within star-forming molecular clouds. However, the strength of their respective line emission in the J=6-5 transitions in APM08279+5255 is extremely high, suggesting that they are excited by another mechanism besides collisions in the dense molecular gas phase alone. We derive J=6-5 line luminosities of L'(HCN)=(4.9+/-0.6), L'(HNC)=(2.4+/-0.7), and L'(HCO+)=(3.0+/-0.6)x10^10 (mu_L)^-1 K km/s pc^2 (where mu_L is the lensing magnification factor), corresponding to L' ratios of ~0.23-0.46 relative to CO(J=1-0). Such high line ratios would be unusual even in the respective ground-state (J=1-0) transitions, and indicate exceptional, collisionally and radiatively driven excitation conditions in the dense, star-forming molecular gas in APM08279+5255. Through an expansion of our previous modeling of the HCN line excitation in this source, we show that the high rotational line fluxes are caused by substantial infrared pumping at moderate opacities in a ~220K warm gas and dust component. This implies that standard M_dense/L' conversion factors would substantially overpredict the dense molecular gas mass M_dense. We also find a HCN J=6-5/5-4 L' ratio greater than 1 (1.36+/-0.31) - however, our models show that the excitation is likely not `super-thermal', but that the high line ratio is due to a rising optical depth between both transitions. These findings are consistent with the picture that the bulk of the gas and dust in this source is situated in a compact, nuclear starburst, where both the highly active galactic nucleus and star formation contribute to the heating.

astro-ph.CO↗

arXiv2010

[CII] line emission in BRI1335-0417 at z=4.4

Using the 12m APEX telescope, we have detected redshifted emission from the 157.74micron [CII] line in the z=4.4074 quasar BRI1335-0417. The linewidth and redshift are in good agreement with previous observations of high-J CO line emission. We measure a [CII] line luminosity, L_[CII] = (16.4 +/- 2.6)x10^9 Lsun, making BRI~1335-0417 the most luminous, unlensed [CII] line emitter known at high-redshift. The [CII]-to-FIR luminosity ratio of (5.3+/-0.8)x10^-4 is ~3x higher than expected for an average object with a FIR luminosity L_FIR = 3.1x10^13 Lsun, if this ratio were to follow the trend observed in other FIR-bright galaxies that have been detected in [CII] line emission. These new data suggest that the scatter in the [CII]-to-FIR luminosity ratio could be larger than previously expected for high luminosity objects. BR1335-0417 has a similar FIR luminosity and [CII]/CO luminosity compared to local ULIRGS and appears to be a gas-rich merger forming stars at a rate of a few thousand solar masses per year.

astro-ph.CO↗

arXiv2010

Cold molecular gas in massive disk galaxies at z=1.5

We report the detection of the CO J=1-0 emission line in three near-infrared selected star-forming galaxies at z~1.5 with the Very Large Array (VLA) and the Green Bank telescope (GBT). These observations directly trace the bulk of molecular gas in these galaxies. We find H_2 gas masses of 8.3 \pm 1.9 x 10^{10} M_sun, 5.6 \pm 1.4 x 10^{10} M_sun and 1.23 \pm 0.34 x 10^{11} M_sun for BzK-4171, BzK-21000 and BzK-16000, respectively, assuming a conversion alpha_CO=3.6 M_sun (K km s^{-1} pc^{2})^{-1}. We combined our observations with previous CO 2-1 detections of these galaxies to study the properties of their molecular gas. We find brightness temperature ratios between the CO 2-1 and CO 1-0 emission lines of 0.80_{-0.22}^{+0.35}, 1.22_{-0.36}^{+0.61} and 0.41_{-0.13}^{+0.23} for BzK-4171, BzK-21000 and BzK-16000, respectively. At the depth of our observations it is not possible to discern between thermodynamic equilibrium or sub-thermal excitation of the molecular gas at J=2. However, the low temperature ratio found for BzK-16000 suggests sub-thermal excitation of CO already at J=2. For BzK-21000, a Large Velocity Gradient model of its CO emission confirms previous results of the low-excitation of the molecular gas at J=3. From a stacked map of the CO 1-0 images, we measure a CO 2-1 to CO 1-0 brightness temperature ratio of 0.92_{-0.19}^{+0.28}. This suggests that, on average, the gas in these galaxies is thermalized up to J=2, has star-formation efficiencies of ~100 L_sun (K km s^{-1} pc^2)^{-1} and gas consumption timescales of ~0.4 Gyr, unlike SMGs and QSOs at high redshifts.

astro-ph.CO↗

arXiv2010

Molecular Gas in Redshift 6 Quasar Host Galaxies

We report our new observations of redshifted carbon monoxide emission from six z~6 quasars, using the PdBI. CO (6-5) or (5-4) line emission was detected in all six sources. Together with two other previous CO detections, these observations provide unique constraints on the molecular gas emission properties in these quasar systems close to the end of the cosmic reionization. Complementary results are also presented for low-J CO lines observed at the GBT and the VLA, and dust continuum from five of these sources with the SHARC-II bolometer camera at the CSO. We then present a study of the molecular gas properties in our combined sample of eight CO-detected quasars at z~6. The detections of high-order CO line emission in these objects indicates the presence of highly excited molecular gas, with estimated masses on the order of 10^10 M_sun within the quasar host galaxies. No significant difference is found in the gas mass and CO line width distributions between our z~6 quasars and samples of CO-detected $1.4\leq z\leq5$ quasars and submillimeter galaxies. Most of the CO-detected quasars at z~6 follow the far infrared-CO luminosity relationship defined by actively star-forming galaxies at low and high redshifts. This suggests that ongoing star formation in their hosts contributes significantly to the dust heating at FIR wavelengths. The result is consistent with the picture of galaxy formation co-eval with supermassive black hole (SMBH) accretion in the earliest quasar-host systems. We investigate the black hole--bulge relationships of our quasar sample, using the CO dynamics as a tracer for the dynamical mass of the quasar host. The results place important constraints on the formation and evolution of the most massive SMBH-spheroidal host systems at the highest redshift.

astro-ph.CO↗

arXiv2009

Constraints on the presence of water megamaser emission in z~2.5 ultraluminous infrared starburst galaxies

We present Expanded Very Large Array and Arecibo observations of two lensed submm galaxies at z~2.5, in order to search for redshifted 22.235 GHz water megamaser emission. Both SMM J14011+0252 and SMM J16359+6612 have multi-wavelength characteristics consistent with ongoing starburst activity, as well as CO line emission indicating the presence of warm molecular gas. Our observations do not reveal any evidence for H2O megamaser emission in either target, while the lensing allows us to obtain deep limits to the H_2O line luminosities, L(H2O) < 7470 Lsun (3-sigma) in the case of SMM J14011+0252, and L(H2O) < 1893 Lsun for SMM J16359+6612, assuming linewidths of 80 km/s. Our search for, and subsequent non-detection of H2O megamaser emission in two strongly lensed starburst galaxies, rich in gas and dust, suggests that such megamaser emission is not likely to be common within the unlensed population of high-redshift starburst galaxies. We use the recent detection of strong H2O megamaser emission in the lensed quasar, MG J0414+0534 at z = 2.64 to make predictions for future EVLA C-band surveys of H2O megamaser emission in submm galaxies hosting AGN.

astro-ph.CO↗

arXiv2009

Radio and X-ray properties of submillimeter galaxies in the A2125 field

We present the radio and X-ray properties of 1.2 mm MAMBO source candidates in a 1600 sq. arcmin field centered on the Abell 2125 galaxy cluster at z=0.247. The brightest, non-synchrotron mm source candidate in the field has a photometric redshift, z = 3.93^+1.11_-0.80, and is not detected in a 31 ks Chandra X-ray exposure. These findings are consistent with this object being an extremely dusty and luminous starburst galaxy at high-redshift, possibly the most luminous yet identified in any blank-field mm survey. The deep 1.4 GHz VLA imaging identifies counterparts for 83% of the 29 mm source candidates identified at >=4-sigma S(1.2mm) = 2.7 - 52.1 mJy, implying that the majority of these objects are likely to lie at z <~ 3.5. The median mm-to-radio wavelength photometric redshift of this radio-detected sample is z~2.2 (first and third quartiles of 1.7 and 3.0), consistent with the median redshift derived from optical spectroscopic surveys of the radio-detected subsample of bright submm galaxies (S(850um) > 5 mJy). Three mm-selected quasars are confirmed to be X-ray luminous in the high resolution Chandra imaging, while another mm source candidate with potential multiple radio counterparts is also detected in the X-ray regime. Both of these radio counterparts are positionally consistent with the mm source candidate. One counterpart is associated with an elliptical galaxy at z = 0.2425, but we believe that a second counterpart associated with a fainter optical source likely gives rise to the mm emission at z~1.

astro-ph.CO↗

arXiv2009

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.

astro-ph.CO↗