skip to main content

Attention:

The NSF Public Access Repository (NSF-PAR) system and access will be unavailable from 11:00 PM ET on Thursday, May 23 until 2:00 AM ET on Friday, May 24 due to maintenance. We apologize for the inconvenience.


Search for: All records

Creators/Authors contains: "Harrison, C. M."

Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher. Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?

Some links on this page may take you to non-federal websites. Their policies may differ from this site.

  1. ABSTRACT

    Deep radio surveys of extragalactic legacy fields trace a large range of spatial and brightness temperature sensitivity scales, and therefore have differing biases to radio-emitting physical components within galaxies. This is particularly true of radio surveys performed at $\lesssim 1 \ \mathrm{arcsec}$ angular resolutions, and so robust comparisons are necessary to better understand the biases present in each survey. We present a multiresolution and multiwavelength analysis of the sources detected in a new Very Long Baseline Array (VLBA) survey of the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey Great Observatories Origins Deep Survey-North field. For the 24 VLBA-selected sources described in Paper I, we augment the VLBA data with EVN data, and ∼0.1–1 arcsec angular resolution data provided by Very Large Array (VLA) and enhanced-Multi Element Remotely Linked Interferometry Network. This sample includes new active galactic nuclei (AGN) detected in this field, thanks to a new source extraction technique that adopts priors from ancillary multiwavelength data. The high brightness temperatures of these sources (TB ≳ 106 K) confirm AGN cores, that would often be missed or ambiguous in lower-resolution radio data of the same sources. Furthermore, only 15 sources are identified as ‘radiative’ AGN based on available X-ray and infrared constraints. By combining VLA and VLBA measurements, we find evidence that the majority of the extended radio emission is also AGN dominated, with only three sources with evidence for extended potentially star formation-dominated radio emission. We demonstrate the importance of wide-field multiresolution (arcsecond–milliarcsecond) coverage of the faint radio source population, for a complete picture of the multiscale processes within these galaxies.

     
    more » « less
  2. ABSTRACT

    We present a comprehensive study of the molecular gas properties of 17 Type 2 quasars at z < 0.2 from the Quasar Feedback Survey (L$_{\rm [O~{\small III}]}$ > 1042.1 $\rm ergs^{-1}$), selected by their high [O iii] luminosities and displaying a large diversity of radio jet properties, but dominated by LIRG-like galaxies. With these data, we are able to investigate the impact of AGN and AGN feedback mechanisms on the global molecular interstellar medium. Using Atacama Pathfinder EXperiment and ALMA ACA observations, we measure the total molecular gas content using the CO(1-0) emission and homogeneously sample the carbon monoxide (CO) spectral line energy distributions, observing CO transitions (Jup  = 1, 2, 3, 6, 7). We observe high r21 ratios (r21  = L’CO(2-1)/L’CO(1-0)) with a median r21  = 1.06, similar to local (U)LIRGs (with r21 ∼ 1) and higher than normal star-forming galaxies (with r21 ∼ 0.65). Despite the high r21 values, for the seven targets with the required data, we find low excitation in CO(6-5) & CO(7-6) (r61 and r62 < 0.6 in all but one target), unlike high-redshift quasars in the literature, which are far more luminous and show higher line ratios. The ionized gas traced by [O iii] exhibits systematically higher velocities than the molecular gas traced by CO. We conclude that any effects of quasar feedback (e.g. via outflows and radio jets) do not have a significant instantaneous impact on the global molecular gas content and excitation and we suggest that it only occurs on more localized scales.

     
    more » « less
  3. ABSTRACT

    We present a study of molecular gas, traced via CO (3–2) from Atacama Large Millimeter/submillimeter Array data, of four z < 0.2, ‘radio quiet’, type 2 quasars (Lbol ∼ 1045.3–1046.2 erg s−1; L$_{\mathrm{1.4\, GHz}}\sim 10^{23.7}\!-\!10^{24.3}$ W Hz−1). Targets were selected to have extended radio lobes (≥ 10 kpc), and compact, moderate-power jets (1–10 kpc; Pjet ∼ 1043.2–1043.7 erg s−1). All targets show evidence of central molecular outflows, or injected turbulence, within the gas discs (traced via high-velocity wing components in CO emission-line profiles). The inferred velocities (Vout = 250–440 km s−1) and spatial scales (0.6–1.6 kpc), are consistent with those of other samples of luminous low-redshift active galactic nuclei. In two targets, we observe extended molecular gas structures beyond the central discs, containing 9–53  per cent of the total molecular gas mass. These structures tend to be elongated, extending from the core, and wrap-around (or along) the radio lobes. Their properties are similar to the molecular gas filaments observed around radio lobes of, mostly ‘radio loud’, brightest cluster galaxies. They have the following: projected distances of 5–13 kpc; bulk velocities of 100–340 km s−1; velocity dispersion of 30–130 km s−1; inferred mass outflow rates of 4–20 M⊙ yr−1; and estimated kinetic powers of 1040.3–1041.7 erg s−1. Our observations are consistent with simulations that suggest moderate-power jets can have a direct (but modest) impact on molecular gas on small scales, through direct jet–cloud interactions. Then, on larger scales, jet-cocoons can push gas aside. Both processes could contribute to the long-term regulation of star formation.

     
    more » « less
  4. ABSTRACT We present the hot molecular and warm ionized gas kinematics for 33 nearby (0.001 ≲ z ≲ 0.056) X-ray selected active galaxies using the H$_2\, 2.1218\, \mu$m and Br γ emission lines observed in the K band with the Gemini near-infrared integral field spectrograph. The observations cover the inner 0.04–2 kpc of each active galactic nucleus at spatial resolutions of 4–250 pc with a velocity resolution of σinst ≈ 20 ${\rm km\, s^{-1}}$. We find that 31 objects (94 per cent) present a kinematically disturbed region (KDR) seen in ionized gas, while such regions are observed in hot molecular gas for 25 galaxies (76 per cent). We interpret the KDR as being due to outflows with masses of 102–107 and 100–104 M⊙ for the ionized and hot molecular gas, respectively. The ranges of mass-outflow rates ($\dot{M}_{\rm out}$) and kinetic power ($\dot{E}_{\rm K}$) of the outflows are 10−3–101 M⊙ yr−1 and ∼1037–1043 erg s−1 for the ionized gas outflows, and 10−5–10−2 M⊙ yr−1 and 1035–1039 erg s−1 for the hot molecular gas outflows. The median coupling efficiency in our sample is $\dot{E}_{\mathrm{K}}/L_{\rm bol}\approx 1.8\times 10^{-3}$ and the estimated momentum fluxes of the outflows suggest they are produced by radiation-pressure in low-density environment, with possible contribution from shocks. 
    more » « less
  5. ABSTRACT

    We present the first eight months of data from our secondary target programme within the ongoing Dark Energy Spectroscopic Instrument (DESI) survey. Our programme uses a mid-infrared and optical colour selection to preferentially target dust-reddened quasi-stellar objects (QSOs) that would have otherwise been missed by the nominal DESI QSO selection. So far, we have obtained optical spectra for 3038 candidates, of which ∼70 per cent of the high-quality objects (those with robust redshifts) are visually confirmed to be Type 1 QSOs, consistent with the expected fraction from the main DESI QSO survey. By fitting a dust-reddened blue QSO composite to the QSO spectra, we find they are well-fitted by a normal QSO with up to AV ∼ 4 mag of line-of-sight dust extinction. Utilizing radio data from the LOFAR Two-metre Sky Survey (LoTSS) DR2, we identify a striking positive relationship between the amount of line-of-sight dust extinction towards a QSO and the radio detection fraction, that is not driven by radio-loud systems, redshift and/or luminosity effects. This demonstrates an intrinsic connection between dust reddening and the production of radio emission in QSOs, whereby the radio emission is most likely due to low-powered jets or winds/outflows causing shocks in a dusty environment. On the basis of this evidence, we suggest that red QSOs may represent a transitional ‘blow-out’ phase in the evolution of QSOs, where winds and outflows evacuate the dust and gas to reveal an unobscured blue QSO.

     
    more » « less
  6. ABSTRACT

    We present results from a combined radio polarization and emission-line study of five type 2 quasars at z < 0.2 with the Karl G. Jansky Very Large Array (VLA) B-array at 5 GHz and Hubble Space Telescope (HST) [O iii] observations. These five sources are known to exhibit close association between radio structures and ionized gas morphology and kinematics. Four sources (J0945+1737, J1000+1242, J1356+1026, and J1430+1339) show polarization in the current data. J1010+1413 is the unpolarized source in our sample. We detect $0.5{-}1{{\ \rm per\ cent}}$ fractional polarization in the radio cores and a high fractional polarization ($10{-}30{{\ \rm per\ cent}}$) in the lobes of these sources. The morphological, spectral, and polarization properties suggest a jet origin for radio emission in J0945+1737, J1000+1242, J1010+1413, and J1430+1339 whereas the current data cannot fully discern the origin of radio emission (jet or wind) in J1356+1026. An anticorrelation between various polarized knots in the radio and [O iii] emission is observed in our sources, similar to that observed in some radio-loud AGN in the literature. This suggests that the radio emission is likely to be depolarized by the emission-line gas. By modelling the depolarization effects, we estimate the size of the emission-line gas clouds to be ∼(2.8 ± 1.7) × 10−5 parsec and the amount of thermal material mixed with the synchrotron plasma to be ∼(1.01 ± 0.08) × 106 M⊙ in the lobe of J0945+1737 (which exhibits the most prominent polarization signature in its lobe). The current work demonstrates that the interplay of jets/winds and emission-line gas is most likely responsible for the nature of radio outflows in radio-quiet AGN.

     
    more » « less
  7. ABSTRACT

    We study the gas distribution and kinematics of the inner kpc of six moderately luminous (43.43 ≤ log Lbol ≤ 44.83) nearby (0.004 ≤ z ≤ 0.014) Seyfert galaxies observed with the Near-infrared Integral Field Spectrograph (NIFS) in the J ($1.25\,\mu$m) and K ($2.2\,\mu$m) bands. We analyse the most intense emission lines detected on these spectral wavebands: [Fe ii] $1.2570\, \mu$m and Paβ, which trace the ionized gas in the partially and fully ionized regions, and $\mathrm{ H}_2 \ 2.1218\, \mu$m, which traces the hot (∼2000 K) molecular gas. The dominant kinematic component is rotation in the disc of the galaxies, except for the ionized gas in NGC 5899 that shows only weak signatures of a disc component. We find ionized gas outflow in four galaxies, while signatures of H2 outflows are seen in three galaxies. The ionized gas outflows display velocities of a few hundred km s−1, and their mass outflow rates are in the range 0.005–12.49 M⊙ yr−1. Their kinetic powers correspond to 0.005–0.7 per cent of the active galactic nuclei (AGN) bolometric luminosities. Besides rotation and outflows signatures in some cases, the H2 kinematics also reveals inflows in three galaxies. The inflow velocities are 50–80 km s−1 and the mass inflow rates are in the range 1–9 × 10−4 M⊙ yr−1 for hot molecular gas. These inflows might be only the hot skin of the total inflowing gas, which is expected to be dominated by colder gas. The mass inflow rates are lower than the current accretion rates to the AGN, and the ionized outflows are apparently disturbing the gas in the inner kpc.

     
    more » « less