arXiv subjects

Andrew Humphrey

Publications and source records attributed to Andrew Humphrey.

27 records · Page 2Linked to original sources

arXiv2015

CALIFA Spectroscopy of the Interacting Galaxy NGC 5394 (Arp 84): Starbursts, Enhanced [NII]6584 and Signs of Outflows and Shocks

We investigate the spiral galaxy NGC 5394, which is strongly interacting with the larger spiral NGC 5395 (the pair is Arp 84), using optical integral-field spectroscopy from the CALIFA survey. Spatially-resolved equivalent-widths, emission-line ratios and kinematics reveal many features related to the interaction, which has reshaped the galaxy. $\rm Hα$ maps (with other diagnostic emission lines) show a concentrated central ($r<1$ kpc) starburst and three less luminous star-forming regions (one knot far out in the northern arm), and we estimate the dust-corrected total star-formation rate as 3.39 $\rm M_{\odot}yr^{-1}$. However, much of the galaxy, especially the outer tidal arms, has a post-starburst spectrum, evidence of a more extensive episode of star-formation a few $\times 10^8$ yr ago, triggered by the previous perigalacticon. The $\rm [NII]6584/Hα$ ratio is high in the nucleus, reaching 0.63 at the centre, which we interpret as related to high electron density ($n_e\simeq 750$ $\rm cm^{-3}$ from the $\rm [SII]{6717\over 6731}$ ratio). We find a central region of strong and blueshifted NaI(5890,5896) absorption, indicative of a starburst-driven outflow from the nucleus at an estimated velocity $\sim 223$ km $\rm s^{-1}$. The CALIFA data also show an annular region at radii 2.25--4 kpc from the nucleus, with elevated ratios of [NII], [OI]6300 etc. to the Balmer lines -- this is evidence of shock excitation, which might be the result of interaction-triggered gas inflow.

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arXiv2014

Spectroscopy of 7 Radio-Loud QSOs at 2<z<6: Giant Lyman-alpha Nebulae Accreting onto Host Galaxies

We performed long-slit optical spectroscopy (GTC-OSIRIS) of 6 radio-loud QSOs at redshifts $2<z<3$, known to have giant ($\sim 50$-100 kpc) Lyman-$α$ emitting nebulae, and detect extended Lyman-$α$ emission for 4, with surface brightness $\sim10^{-16}$ ergs $\rm cm^{-2}s^{-1}arcsec^{-2}$ and line width FWHM 400-1100 (mean 863) km $\rm s^{-1}$. We also observed the $z\simeq 5.9$ radio-loud QSO, SDSS J2228+0110, and find evidence of a $\geq 10$ kpc extended Lyman-$α$ emission nebula, a new discovery for this high-redshift object. Spatially-resolved kinematics of the 5 nebulae are examined by fitting the Lyman-$α$ wavelength at a series of positions along the slit. We found the line-of-sight velocity $Δ(v)$ profiles to be relatively flat. However, 3 of the nebulae appear systematically redshifted by 250-460 km $\rm s^{-1}$ relative to the Lyman-$α$ line of the QSO (with no offset for the other two), which we argue is evidence for infall. One of these (Q0805+046) had a small ($\sim 100$ km $\rm s^{-1}$) velocity shift across its diameter and a steep gradient at the centre. Differences in line-of-sight kinematics between these 5 giant nebulae and similar nebulae associated with high-redshift radio galaxies (which can show steep velocity gradients) may be due to an orientation effect, which brings infall/outflow rather than rotation into greater prominence for the sources observed `on-axis' as QSOs.

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arXiv2014

Extreme CII emission in type 2 quasars at z~2.5: a signature of kappa-distributed electron energies?

We investigate the flux ratio between the 1335 A and 2326 A lines of singly ionized carbon in the extended narrow line regions of type 2 quasars at z~2.5. We find the observed CII 1335 / CII] 2326 flux ratio, which is not sensitive to the C/H abundance ratio, to be often several times higher than predicted by the canonical AGN photoionization models that use solar metallicity and a Maxwell-Boltzmann electron energy distribution. We study several potential solutions for this discrepancy: low gas metallicity, shock ionization, continuum fluorescence, and kappa-distributed electron energies. Although we cannot definitively distinguish between several of the proposed solutions, we argue that a kappa distribution gives the more natural explanation. We also provide a grid of AGN photoionization models using kappa-distributed electron energies.

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arXiv2013

Enhanced Nitrogen in Morphologically Disturbed Blue Compact Galaxies at 0.20 < z < 0.35: Probing Galaxy Merging Features

We present a study of correlations between the elemental abundances and galaxy morphologies of 91 blue compact galaxies (BCGs) at z=0.20-0.35 with Sloan Digital Sky Survey (SDSS) DR7 data. We classify the morphologies of the galaxies as either 'disturbed' or 'undisturbed', by visual inspection of the SDSS images, and using the Gini coefficient and M_20. We derive oxygen and nitrogen abundances using the T_e method. We find that a substantial fraction of BCGs with disturbed morphologies, indicative of merger remnants, show relatively high N/O and low O/H abundance ratios. The majority of the disturbed BCGs exhibit higher N/O values at a given O/H value compared to the morphologically undisturbed galaxies, implying more efficient nitrogen enrichment in disturbed BCGs. We detect Wolf-Rayet (WR) features in only a handful of the disturbed BCGs, which appears to contradict the idea that WR stars are responsible for high nitrogen abundance. Combining these results with Galaxy Evolution Explorer (GALEX) GR6 ultraviolet (UV) data, we find that the majority of the disturbed BCGs show systematically lower values of the H alpha to near-UV star formation rate ratio. The equivalent width of the H beta emission line is also systematically lower in the disturbed BCGs. Based on these results, we infer that disturbed BCGs have undergone star formation over relatively longer time scales, resulting in a more continuous enrichment of nitrogen. We suggest that this correlation between morphology and chemical abundances in BCGs is due to a difference in their recent star formation histories.

astro-ph.CO↗

arXiv2012

A massive bubble of extremely metal poor gas around a collapsing Ly-alpha blob at z=2.54

Using long-slit optical spectroscopy obtained at the 10.4 m Gran Telescopio Canarias, we have examined the gaseous environment of the radio-loud quasar TXS 1436+157 (z=2.54), previously known to be associated with a large Ly-alpha nebula and a spatially extended Ly-alpha-absorbing structure. From the Ly-alpha nebula we measure kinematic properties consistent with infall at a rate of about 10-100 M./yr - more than sufficient to power a quasar at the top of the luminosity function. The absorbing structure lies outside of the Ly-alpha nebula, at a radius of >40 kpc from the quasar. Against the bright unresolved continuum and line emission from the quasar, we detect in absorption the NV 1239,1241, CIV 1548,1551 and SiIV 1394,1403 doublets, with no unambiguous detection of absorption lines from any low-ionization species of metal. The metal column densities, taken together with the HI column density measurement from the literature, indicate that the absorbing gas is predominantly ionized by the quasar, has a mass of hydrogen of >1.6 x 10E11 M., a gas density of <18 per cubic cm, a line of sight thickness of >18 pc, and a covering factor approaching unity. While this absorbing structure is clearly not composed of pristine gas, it has an extremely low metallicity, with ionization models providing a 3-sigma limit of 12+log(O/H)<7.3. To explain these results, we discuss a scenario involving starburst-driven super-bubbles and the creation of infalling filaments of cold gas which fuel/trigger the quasar. We also discuss the possibility of detecting large-scale absorbers such as this in emission when illuminated by a powerful quasar.

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arXiv2009

Accretion/Jet Activity and Narrow [O III] Kinematics in Young Radio Galaxies

We estimate black hole masses and Eddington ratios for a sample of 81 young radio galaxies (42 CSS +39 GPS). We find that the average black hole (BH) mass of these young radio galaxies is ~8.3, which is less than that of radio loud QSOs and low redshift radio galaxies. The CSS/GPS sources have relatively high Eddington ratios, with an average value of =-0.75, which are similar to those of narrow line Seyfert 1 galaxies (NLS1s). This suggests that young radio galaxies may not only be in the early stages of their radio activity, but also in the early stage of their accretion activity. We find that the young radio galaxies as a class deviate systematically from M_bh-σrelation defined by nearby inactive galaxies, when using [O III] as a surrogate for stellar velocity dispersion, σ_* . We also find that the deviation of the [O III] line width is correlated with the Eddington ratio and sources with Lbol/LEdd~1 have the largest deviations, which are similar to those of radio quiet QSOs/NLS1s (radio jets is absent or weak). A similar result has been obtained for 9 linear radio Seyfert galaxies. On the basis of these results, we suggest that, in addition to the possible jet-gas interactions, accretion activities may also play an important role in shaping the kinematics of the narrow [O III] line in young radio galaxies and linear radio Seyferts.

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arXiv2009

A New Application of the Astrometric Method to Break Severe Degeneracies in Binary Microlensing Events

When a source star is microlensed by one stellar component of a widely separated binary stellar components, after finishing the lensing event, the event induced by the other binary star can be additionally detected. In this paper, we investigate whether the close/wide degeneracies in binary lensing events can be resolved by detecting the additional centroid shift of the source images induced by the secondary binary star in wide binary lensing events. From this investigation, we find that if the source star passes close to the Einstein ring of the secondary companion, the degeneracy can be easily resolved by using future astrometric follow-up observations with high astrometric precision. We determine the probability of detecting the additional centroid shift in binary lensing events with high magnification. From this, we find that the degeneracy of binary lensing events with a separation of $\lesssim 20.0$ AU can be resolved with a significant efficiency. We also estimate the waiting time for the detection of the additional centroid shift in wide binary lensing events. We find that for typical Galactic lensing events with a separation of $\lesssim 20.0$ AU, the additional centroid shift can be detected within 100 days, and thus the degeneracy of those events can be sufficiently broken within a year.

astro-ph.SR↗

arXiv2008

Emission line activity in type 2 quasars from the Sloan Digital Sky Survey

We have compared the optical emission line ratios of type 2 quasars from Zakamska et al. with standard AGN photoionization model predictions, Seyfert 2s, HII galaxies, and narrow line FRII radio galaxies. Moderate to high ionization narrow line radio galaxies and Seyfert 2s are indistinguishable from type 2 quasars based on their optical line ratios. The standard AGN photoionization models, widely discussed for other type 2 AGNs, can reproduce successfully the loci and trends of type 2 quasars in some of the main diagnostic diagrams. These models are not exempt of problems and the discrepancies with the data are the same encountered for other type 2 AGNs. As for these, realistic models must take into account a range of cloud properties, as widely demonstrated in the literature. We also study the possible impact of stellar photoionization.

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arXiv2007

Energy distribution of individual quasars from far-UV to X-rays: I. Intrinsic UV hardness and dust opacities

Using Chandra and HST archival data, we have studied the individual Spectral Energy Distribution (SED) of 11 quasars. All UV spectra show a spectral break around 1100A. 5 X-ray spectra show the presence of a ``soft excess'' and 7 spectra showed an intrinsic absorption. We found that for most quasars a simple extrapolation of the far-UV powerlaw into the X-ray domain generally lies below the X-ray data and that the big blue bump and the soft X-ray excess do not share a common physical origin. We explore the issue of whether the observed SED might be dust absorbed in the far and near-UV. We fit the UV break, assuming a powerlaw that is absorbed by cubic nanodiamond dust grains. We then explore the possibility of a universal SED (with a unique spectral index) by including further absorption from SMC-like extinction. Using this approach, satisfactory fits to the spectra can be obtained. The hydrogen column densities required by either nanodiamonds or amorphous dust models are all consistent, except for one object, with the columns deduced by our X-ray analysis, provided that the C depletion is ~0.6. Because dust absorption implies a flux recovery in the extreme UV (<700A), our modeling opens the possibility that the intrinsic quasar SED is much harder and more luminous in the extreme UV than inferred from the near-UV data, as required by photoionization models of the broad emission line region. We conclude that the intrinsic UV SED must undergo a sharp turn-over before the X-ray domain.

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