arXiv subjects

A. Humphrey

Publications and source records attributed to A. Humphrey.

At least 55 records · Page 3Linked to original sources

arXiv2015

VLT-FORS2 optical imaging and spectroscopy of 9 luminous type 2 AGN at 0.3<z<0.6: I. Ionized gas nebulae

We present optical imaging and long slit spectroscopic observations of 9 luminous type 2 AGNs within the redshift range 0.3<z<0.6 based on VLT-FORS2 data. Most objects (6/9) are high luminosity Seyfert 2, and three are type 2 quasars (QSO2), with our sample extending to lower luminosity than previous works. Seven out of nine objects (78%) show morphological evidence for interactions or mergers in the form of disturbed morphologies and/or peculiar features such as tidal tails, amorphous halos, or compact emission line knots. The detection rate of morphological evidence for interaction is consistent with those found during previous studies of QSO2 at similar z, suggesting that the merger rate is independent of AGN power at the high end of the AGN luminosity function. We find the emission line flux spatial profiles are often dominated by the often spatially unresolved central source. In addition, all but one of our sample is associated with much fainter, extended line emission. We find these extended emission line structures have a variety of origins and ionization mechanisms: star forming companions, tidal features, or extended ionized nebulae. AGN related processes dominate the excitation of the nuclear gas. Stellar photoionization sometimes plays a role in extended structures often related to mergers/interactions.

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arXiv2015

GTC optical imaging of extremely red 5C radio galaxies at high redshift

We investigate the nature of seven unusual radio galaxies from the 5C catalogue that were previously known to have extremely red R-K colours, and for which emission lines were previously found to be weak or absent in their optical spectra. We present and discuss u, g, or r images of these radio galaxies, obtained using the Optical System for Imaging and low-Intermediate-Resolution Integrated Spectroscopy (OSIRIS) at the Gran Telescopio Canarias (GTC). We have detected all seven targets in our g-band imaging. Their optical emission is extended, and we tentatively detect a radio-optical alignment effect in this sample. A subset of our sample (three sources) shows broad-band spectral energy distributions that flatten out near the wavelength range of the g-band, implying a dominant contribution there due to young stars and/or scattered or reprocessed radiation from the active nucleus.

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arXiv2015

Witnessing the transformation of a quasar host galaxy at z=1.6

A significant minority of high redshift radio galaxy (HzRG) candidates show extremely red broad band colours and remain undetected in emission lines after optical `discovery' spectroscopy. In this paper we present deep GTC optical imaging and spectroscopy of one such radio galaxy, 5C 7.245, with the aim of better understanding the nature of these enigmatic objects. Our g-band image shows no significant emission coincident with the stellar emission of the host galaxy, but does reveal faint emission offset by ~3" (26 kpc) therefrom along a similar position angle to that of the radio jets, reminiscent of the `alignment effect' often seen in the optically luminous HzRGs. This offset g-band source is also detected in several UV emission lines, giving it a redshift of 1.609, with emission line flux ratios inconsistent with photoionization by young stars or an AGN, but consistent with ionization by fast shocks. Based on its unusual gas geometry, we argue that in 5C 7.245 we are witnessing a rare (or rarely observed) phase in the evolution of quasar hosts when stellar mass assembly, accretion onto the back hole, and powerful feedback activity has eradicated its cold gas from the central ~20 kpc, but is still in the process of cleansing cold gas from its extended halo.

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arXiv2014

The triggering mechanism and properties of ionized outflows in the nearest obscured quasars

We have identified ionized outflows in the narrow line region of all but one SDSS type 2 quasars (QSO2) at z<~0.1 (20/21, detection rate 95%), implying that this is a ubiquitous phenomenon in this object class also at the lowest z. The outflowing gas has high densities (n_e>1000 cm-3) and covers a region the size of a few kpc. This implies ionized outflow masses M~(0.3-2.4)x1e6 Msun and mass outflow rates M(dot)<few Msun yr-1. The triggering mechanism of the outflows is related to the nuclear activity. The QSO2 can be classified in two groups according to the behavior and properties of the outflowing gas. QSO2 in Group 1 (5/20 objects) show the most extreme turbulence, they have on average higher radio luminosities and higher excess of radio emission. QSO2 in Group 2 (15/20 objects) show less extreme turbulence, they have lower radio luminosities and, on average, lower or no radio excess. We propose that two competing outflow mechanisms are at work: radio jets and accretion disk winds. Radio jet induced outflows are dominant in Group 1, while disk winds dominate in Group 2. We find that the radio jet mode is capable of producing more extreme outflows. To test this interpretation we predict that: 1) high resolution VLBA imaging will reveal the presence of jets in Group 1 QSO2; 2) the morphology of their extended ionized nebulae must be more highly collimated and kinematically perturbed.

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arXiv2014

The molecular gas content of ULIRG type 2 quasars at z < 1

We present new results of CO(1-0) spectroscopic observations of 4 SDSS type 2 quasars (QSO2) at z$\sim$0.3, observed with the 30m IRAM telescope. The QSO2 have infrared luminosities in the ULIRG (UltraLuminous Infrared Galaxies) regime. We confirm the CO(1-0) detection in one of our 4 QSO2, SDSS J1543-00, with $L'_{CO}$ and $M_{H_2}$ (1.2$\pm$0.2) $\times$10$^{10}$ K km s$^{-1}$ pc$^2$ and (9.4$\pm$1.4)$\times$10$^9$ M$_{\odot}$, respectively. The CO(1-0) line has $FWHM=$575$\pm$102 km s$^{-1}$. No CO(1-0) emission is detected in SDSS J0903+02, SDSS J1337-01, SDSS J1520-01 above 3 sigma, yielding upper limits on $M(H_2)\sim$ 9.6, 4.3 and 5.1 $\times$10$^9$ M$_{\odot}$ respectively. Together with CO measurements of 9 QSO2 at $z\sim$0.3-1.0 from the ULIRG sample by Combes et al. (2011, 2013), we expand previous studies of the molecular gas content of intermediate $z$ QSO2 into the ULIRG regime. We discuss the location of the 13 ULIRG QSO2 at $z<$1 with available $L'_{CO}$ measurements in the $L'_{CO}$ vs. $z$ and $L'_{CO}$ vs. $L_{FIR}$ diagrams, in comparison with other QSO1 and ULIRG star forming samples.

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arXiv2013

CO(1-0) survey of high-z radio galaxies: alignment of molecular halo gas with distant radio sources

We present a CO(1-0) survey for cold molecular gas in a representative sample of 13 high-z radio galaxies (HzRGs) at 1.4<z<2.8, using the Australia Telescope Compact Array. We detect CO(1-0) emission associated with five sources: MRC 0114-211, MRC 0152-209, MRC 0156-252, MRC 1138-262 and MRC 2048-272. The CO(1-0) luminosities are in the range $L'_{\rm CO} \sim (5 - 9) \times 10^{10}$ K km/s pc$^{2}$. For MRC 0152-209 and MRC 1138-262 part of the CO(1-0) emission coincides with the radio galaxy, while part is spread on scales of tens of kpc and likely associated with galaxy mergers. The molecular gas mass derived for these two systems is M$_{\rm H2} \sim 6 \times 10^{10}\, {\rm M}_{\odot}$ (M$_{\rm H2}$/$L'_{\rm CO}$=0.8). For the remaining three CO-detected sources, the CO(1-0) emission is located in the halo (~50-kpc) environment. These three HzRGs are among the fainter far-IR emitters in our sample, suggesting that similar reservoirs of cold molecular halo gas may have been missed in earlier studies due to pre-selection of IR-bright sources. In all three cases the CO(1-0) is aligned along the radio axis and found beyond the brightest radio hot-spot, in a region devoid of 4.5$μ$m emission in Spitzer imaging. The CO(1-0) profiles are broad, with velocity widths of ~ 1000 - 3600 km/s. We discuss several possible scenarios to explain these halo reservoirs of CO(1-0). Following these results, we complement our CO(1-0) study with detections of extended CO from the literature and find at marginal statistical significance (95% level) that CO in HzRGs is preferentially aligned towards the radio jet axis. For the eight sources in which we do not detect CO(1-0), we set realistic upper limits of $L'_{\rm CO} \sim 3-4 \times 10^{10}$ K km/s pc$^{2}$. Our survey reveals a CO(1-0) detection rate of 38%, allowing us to compare the CO(1-0) content of HzRGs with that of other types of high-z galaxies.

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arXiv2013

Extremely Metal-Poor Galaxies: The HI Content

Extremely metal-poor (XMP) galaxies are chemically, and possibly dynamically, primordial objects in the local Universe. Our objective is to characterize the HI content of the XMP galaxies as a class, using as a reference the list of 140 known local XMPs compiled by Morales-Luis et al. (2011). We have observed 29 XMPs, which had not been observed before at 21 cm, using the Effelsberg radio telescope. This information was complemented with HI data published in literature for a further 53 XMPs. In addition, optical data from the literature provided morphologies, stellar masses, star-formation rates and metallicities. Effelsberg HI integrated flux densities are between 1 and 15 Jy km/s, while line widths are between 20 and 120 km/s. HI integrated flux densities and line widths from literature are in the range 0.1 - 200 Jy km/s and 15 - 150 km/s, respectively. Of the 10 new Effelsberg detections, two sources show an asymmetric double-horn profile, while the remaining sources show either asymmetric (7 sources) or symmetric (1 source) single-peak 21 cm line profiles. An asymmetry in the HI line profile is systematically accompanied by an asymmetry in the optical morphology. Typically, the g-band stellar mass-to-light ratios are ~0.1, whereas the HI gas mass-to-light ratios may be up to 2 orders of magnitude larger. Moreover, HI gas-to-stellar mass ratios fall typically between 10 and 20, denoting that XMPs are extremely gas-rich. We find an anti-correlation between the HI gas mass-to-light ratio and the luminosity, whereby fainter XMPs are more gas-rich than brighter XMPs, suggesting that brighter sources have converted a larger fraction of their HI gas into stars. The dynamical masses inferred from the HI line widths imply that the stellar mass does not exceed 5% of the dynamical mass, while the \ion{H}{i} mass constitutes between 20 and 60% of the dynamical mass. (abridged)

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arXiv2013

Molecular gas in type 2 quasars at z~0.2-0.3

We present results of CO(1-0) spectroscopic observations of 10 SDSS type 2 quasars (QSO2) at z~0.2-0.3 observed with the 30m IRAM radiotelescope and the Australia Telescope Compact Array. We report 5 new confirmed CO(1-0) detections and 1 tentative detection. They have L'(CO)~several x 1e9 K km s-1 pc^2, while upper limits for the non detections are L'(CO)<~ several x 1e9 K km s-1 pc^2. This study increases the total number of QSO2 with CO measurements at z<~1 to 20, with a 50% detection rate.

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arXiv2013

Polarized extended Ly-alpha emission from a z=2.3 radio galaxy

We present spatially resolved spectropolarimetic measurements of the 100-kpc scale gaseous environment of the z=2.34 radio galaxy TXS 0211-122. The polarization level of the narrow Ly-alpha emission is low centrally (P<5 %), but rises to P=16.4+/-4.6 % in the Eastern part of the nebula, indicating that the nebula is at least partly powered by the scattering of Ly-alpha photons by HI. Not only is this the first detection of polarized Ly-alpha around a radio-loud active galaxy, it is also the second detection to date for any kind of Ly-alpha nebula. We also detect a pair of diametrically opposed UV continuum sources along the slit, at the outer edges of the Ly-alpha nebula, which we suggest may be the limb of a dusty shell, related to the large-scale HI absorbers often associated with high-z radio galaxies.

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arXiv2011

AzTEC 1.1 mm Observations of the MBM12 Molecular Cloud

We present 1.1 mm observations of the dust continuum emission from the MBM12 high-latitude molecular cloud observed with the Astronomical Thermal Emission Camera (AzTEC) mounted on the James Clerk Maxwell Telescope on Mauna Kea, Hawaii. We surveyed a 6.34 deg$^2$ centered on MBM12, making this the largest area that has ever been surveyed in this region with submillimeter and millimeter telescopes. Eight secure individual sources were detected with a signal-to-noise ratio of over 4.4. These eight AzTEC sources can be considered to be real astronomical objects compared to the other candidates based on calculations of the false detection rate. The distribution of the detected 1.1 mm sources or compact 1.1 mm peaks is spatially anti-correlated with that of the 100 micronm emission and the $^{12}$CO emission. We detected the 1.1 mm dust continuum emitting sources associated with two classical T Tauri stars, LkHalpha262 and LkHalpha264. Observations of spectral energy distributions (SEDs) indicate that LkHalpha262 is likely to be Class II (pre-main-sequence star), but there are also indications that it could be a late Class I (protostar). A flared disk and a bipolar cavity in the models of Class I sources lead to more complicated SEDs. From the present AzTEC observations of the MBM12 region, it appears that other sources detected with AzTEC are likely to be extragalactic and located behind MBM12. Some of these have radio counterparts and their star formation rates are derived from a fit of the SEDs to the photometric evolution of galaxies in which the effects of a dusty interstellar medium have been included.

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arXiv2011

Ionized outflows in SDSS type 2 quasars at z~0.3-0.6

We have analyzed the spatially integrated kinematic properties of the ionized gas within the inner r ~2). While the quiescent gas shows small or null velocity shifts relative to the systemic velocity, the highly perturbed gas trends to show larger shifts which, moreover, are blueshifts in general. Within a given object, the most perturbed gas trends to have the largest blueshift as well. All together support that the perturbed gas, which is responsible for the blue asymmetries of the line profiles, is outflowing. Although some bias affects the sample, we argue that ionized gas outflows are a common phenomenon in optically selected type 2 quasars at 0.3< z < 0.6.

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arXiv2011

AzTEC 1.1 mm images of 16 radio galaxies at 0.5<z<5.2 and a quasar at z=6.3

We present 1.1 mm observations for a sample of 16 powerful radio galaxies at 0.5<z<5.2 and a radio quiet quasar at z=6.3, obtained using the AzTEC bolometer array mounted on the ASTE or the JCMT. This paper more than doubles the number of high-z radio galaxies imaged at millimetre/sub-millimetre wavelengths. We detect probable millimetre-wave counterparts for 11 of the active galaxies. The 6 active galaxies which do not have a probable millimetre counterpart in our images nevertheless have one or more likely associated millimetric source. Thus, we conclude that powerful (radio-loud) active galaxies at high-z are beacons for finding luminous millimetre/sub-millimetre galaxies at high-z. The flux densities of our AzTEC counterparts imply star formation rates ranging from <200 to ~1300 M./yr. In addition, we find that for the radio galaxoes the 1.1 mm flux density is anticorrelated with the largest angular size of the radio source. We also present new Spitzer imaging observations of several active galaxies in our sample. Combining these with archival data, we examine the mid-infrared colours of our sample. We find that radio galaxies for which we have detected a probable 1.1 mm counterpart have mid-infrared colours consistent with dusty starbursts, and are usually bluer than high-z Spitzer-selected active galaxies. In addition, we find arcs of 24 micron sources extending across ~200-500 kpc, apparently associated with three of the radio galaxies.

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arXiv2011

Interactions, star formation and extended nebulae in SDSS type 2 quasars at 0.3<~ z <~ 0.6

We present long-slit spectroscopy and imaging data obtained with FORS2 on the Very Large Telescope of 13 optically selected type 2 quasars at z~0.3-0.6 from the original sample of Zakamska et al. (2003). The sample is likely to be affected by different selection biases. We investigate the evidence for: a) mergers/interactions b) star formation activity in the neighborhood of the quasars and c) extended emission line regions and their nature. Evidence for mergers/interactions is found in 5/13 objects. This is a lower limit for our sample, given the shallowness of most of our continuum images. Although AGN photoionization cannot be totally discarded, line ratios consistent with stellar photoionization are found in general in companion galaxies/knots/nuclei near these same objects. On the contrary, the gas in the neighborhood of the quasar nucleus shows line ratios inconsistent with HII galaxies and typical of AGN photoionized nebulae. A natural scenario to explain the observations is that star formation is ongoing in companion galaxies/knots/nuclei, possibly triggered by the interactions. These systems are, therefore, composite in their emission line properties showing a combination of AGN and star formation features. Extended emission line regions (EELRs) have been found in 7/13 objects, although this fraction might be higher if a complete spatial coverage around the quasars was performed. The sizes vary between few and up to 64 kpc. In general, the EELRs apparently consist of an extended nebula associated with the quasar. In at least one case the EELR is associated with ionized tidal features.

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arXiv2010

Integral field spectroscopy of type-II QSOs at z=0.3-0.4

We present and analyse integral-field observations of six type-II QSOs with z=0.3-0.4, selected from the Sloan Digital Sky Survey (SDSS). Two of our sample are found to be surrounded by a nebula of warm ionized gas, with the largest nebula extending across 8" (40 kpc). Some regions of the extended nebulae show kinematics that are consistent with gravitational motion, while other regions show relatively perturbed kinematics: velocity shifts and line widths too large to be readily explained by gravitational motion. We propose that a ~20 kpc x20 kpc outflow is present in one of the galaxies. Possible mechanisms for triggering the outflow are discussed. In this object, we also find evidence for ionization both by shocks and the radiation field of the AGN.

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arXiv2010

VLT and GTC observations of SDSS J0123+00: a type 2 quasar triggered in a galaxy encounter?

We present long-slit spectroscopy, continuum and [OIII]5007 imaging data obtained with the Very Large Telescope and the Gran Telescopio Canarias of the type 2 quasar SDSS J0123+00 at z=0.399. The quasar lies in a complex, gas-rich environment. It appears to be physically connected by a tidal bridge to another galaxy at a projected distance of ~100 kpc, which suggests this is an interacting system. Ionized gas is detected to a distance of at least ~133 kpc from the nucleus. The nebula has a total extension of ~180 kpc. This is one of the largest ionized nebulae ever detected associated with an active galaxy. Based on the environmental properties, we propose that the origin of the nebula is tidal debris from a galactic encounter, which could as well be the triggering mechanism of the nuclear activity. SDSS J0123+00 demonstrates that giant, luminous ionized nebulae can exist associated with type 2 quasars of low radio luminosities, contrary to expectations based on type 1 quasar studies.

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arXiv2009

The extended ionized gas around the z=2.44 radio galaxy MRC 0406-244: the nature of the superbubbles and the optical line brightness asymmetries

In this letter, we investigate the nature of the dramatic `super-bubble' emission structures associated with the z=2.44 radio galaxy MRC 0406-244, using rest-frame optical spectroscopy and an archival HST NICMOS image. Based on the optical line ratios and the HST morphology, we conclude that the gas in the superbubbles is photoionized by the obscured active nucleus. We suggest that this type of structure might be related to the spatially extended HI absorbers that are detected in front of many high-z radio galaxies. We also suggest that we may be witnessing the destruction of the extended emission line region. In addition, we investigate the nature of the emission line brightness asymmetry in MRC 0406-244: we conclude that this asymmetry is due to an asymmetry in the mass of ionized gas, confirming the scenario of McCarthy, van Breugel & Kapahi, and leading us to reject that of Gopal-Krishna & Wiita.

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arXiv2008

Integral Field Spectroscopy of two radio galaxies at z~2.3

In this article we study the morphology, kinematics and ionization properties of the giant ionized gas nebulae surrounding two high redshift radio galaxies, 4C40.36 (z=2.27) and 4C48.48 (z=2.34).}{Integral Field Spectroscopy observations were taken using the PPAK bundle of the PMAS spectrograph, mounted on the 3.5m on the Calar Alto Observatory, in order to cover a field-of-view of 64" X 72" centered in each radio galaxy. The observations spanned over 5 nights, using two different spectral resolutions (with FWHM~4 AA and ~8 AA respectively), covering the optical wavelength range from ~3700 AA to ~7100 AA, which corresponds to the rest-frame ultraviolet range from ~1100 AA to ~2000 AA >. Various emission lines are detected within this wavelength range, including Lyalpha (1216 AA), NV (1240 AA), CIV (1549 AA), HeII (1640 AA), OIII] (1663 AA) and CIII] (1909Å). The dataset was used to derive the spatial distribution of the flux intensity of each of these lines and the gas kinematics. The properties of the emission lines in the nuclear regions were studied in detail.In agreement with previous studies, we find that both objects are embedded in a large ionized gas nebula, where Ly alpha emission is extended across ~100 kpc or more. The CIV and HeII emission lines are also spatially extended. The nebulae are generally aligned with the radio axis, although we detect emission far from it. In 4C+48.48, there is a band of low Ly-alpha/CIV running perpendicular to the radio axis, at the location of the active nucleus. This feature might be the observational signature of an edge-on disk of neutral gas. The kinematics of both nebulae are inconsistent with stable rotation, although they are not inconsistent with infall or outflow.

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arXiv2008

Spatially extended absorption around the z=2.63 radio galaxy MRC 2025-218: outflow or infall?

We present an investigation into the absorber in front of the z=2.63 radio galaxy MRC 2025-218, using integral field spectroscopy obtained at the Very Large Telescope, and long slit spectroscopy obtained at the Keck II telescope. The properties of MRC 2025-218 are particularly conducive to study the nature of the absorbing gas, i.e., this galaxy shows bright and spatially extended Ly-alpha emission, along with bright continuum emission from the active nucleus. Ly-alpha absorption is detected across ~40x30 kpc^2, has a covering factor of ~1, and shows remarkably little variation in its properties across its entire spatial extent. This absorber is kinematically detached from the extended emission line region (EELR). Its properties suggest that the absorber is outside of the EELR. We derive lower limits to the HI, HII and H column densities for this absorber of 3x10^16, 7x10^17 and 2x10^18 cm^-2, respectively. Moreover, the relatively bright emission from the active nucleus has allowed us to measure a number of metal absorption lines: CI, CII, CIV, NV, OI, SiII, SiIV, AlII and AlIII. The column density ratios are most naturally explained using photoionization by a hard continuum, with an ionization parameter U~0.0005-0.005. Shocks or photoionization by young stars cannot reproduce satisfactorily the measured column ratios. Using the ratio between the SiII* and SiII column densities, we derive a lower limit of >10 cm^-3 for the electron density of the absorber. The data do not allow useful constraints to be placed on the metallicity of the absorber. We consider two possibilities for the nature of this absorber: the cosmological infall of gas, and an outflow driven by supernovae or the radio-jets.

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