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A. C. Edge

Publications and source records attributed to A. C. Edge.

At least 127 records · Page 7Linked to original sources
arXiv2011

EMU: Evolutionary Map of the Universe

EMU is a wide-field radio continuum survey planned for the new Australian Square Kilometre Array Pathfinder (ASKAP) telescope. The primary goal of EMU is to make a deep (rms ~ 10 microJy/beam) radio continuum survey of the entire Southern Sky at 1.3 GHz, extending as far North as +30 degrees declination, with a resolution of 10 arcsec. EMU is expected to detect and catalogue about 70 million galaxies, including typical star-forming galaxies up to z~1, powerful starbursts to even greater redshifts, and AGNs to the edge of the visible Universe. It will undoubtedly discover new classes of object. This paper defines the science goals and parameters of the survey, and describes the development of techniques necessary to maximise the science return from EMU.

astro-ph.CO↗
arXiv2011

Molecular accretion in the core of the galaxy cluster 2A 0335+096

We present adaptive optics-assisted K-band integral field spectroscopy of the central cluster galaxy in 2A 0335+096 (z=0.0349). The H2 v=1-0 S(1) emission is concentrated in two peaks within 600 pc of the nucleus and fainter but kinematically-active emission extends towards the nucleus. The H2 is in a rotating structure which aligns with, and appears to have been accreted from, a stream of H-alpha emission extending over 14 kpc towards a companion galaxy. The projected rotation axis aligns with the 5 GHz radio lobes. This H2 traces the known 1.2E9 Msun CO-emitting reservoir; limits on the Br-gamma emission confirm that the H2 emission is not excited by star formation, which occurs at a rate of less than 1 Msun/yr in this gas. If its accretion onto the black hole can be regulated whilst star formation remains suppressed, the reservoir could last for at least 1 Gyr; the simultaneous accretion of just ~ 5 per cent of the gas could drive a series of AGN outbursts which offset X-ray cooling in the cluster core for the full 1 Gyr. Alternatively, if the regulation is ineffective and the bulk of the H2 accretes within a few orbital periods (25-100 Myr), the resulting 1E62 erg outburst would be among the most powerful cluster AGN outbursts known. In either case, these observations further support cold feedback scenarios for AGN heating.

astro-ph.CO↗
arXiv2011

A very extended molecular web around NGC 1275

We present the first detection of CO emission lines in the Halpha filaments at distances as far as 50 kpc from the centre of the galaxy NGC 1275. This gas is probably dense (>=10E3 cm-3). However, it is not possible to accurately determine the density and the kinetic temperature of this relatively warm gas (Tkin~20-500K) with the current data only. The amount of molecular gas in the filaments is large 10E9 Msun (assuming a Galactic N(H2)/Ico ratio). This is 10% of the total mass of molecular gas detected in this cD galaxy. This gas has large-scale velocities comparable to those seen in Halpha. The origin of the filaments is still unclear, but their formation is very likely linked to the AGN positive feedback (Revaz et al., 2008) that regulates the cooling of the surrounding X-ray-emitting gas as suggested by numerical simulations. We also present high-resolution spectra of the galaxy core. The spatial characteristics of the double-peaked profile suggest that the molecular web of filaments and streamers penetrates down to radii of less than 2 kpc from the central AGN and eventually feed the galaxy nucleus. The mass of gas inside the very central region is ~10E^9 Msun, and is similar to the mass of molecular gas found in the filaments.

astro-ph.CO↗
arXiv2011

Herschel-ATLAS: detection of a far-infrared population around galaxy clusters

We report the detection of a significant excess in the surface density of far-infrared sources from the Herschel-Astrophysical Terahertz Large Area Survey (H-ATLAS) within ~1 Mpc of the centres of 66 optically-selected clusters of galaxies in the SDSS with ~0.25. From the analysis of the multiwavelength properties of their counterparts we conclude that the far-infrared emission is associated with dust-obscured star formation and/or active galactic nuclei within galaxies in the clusters themselves. The excess reaches a maximum at a radius of ~0.8 Mpc, where we find 1.0\pm0.3 S_250um>34 mJy sources on average per cluster above what would be expected for random field locations. If the far-infrared emission is dominated by star formation (as opposed to AGN) then this corresponds to an average star formation rate of ~7 M_sun/yr per cluster in sources with L_IR>5d10 L_sun. Although lensed sources make a negligible contribution to the excess signal, a fraction of the sources around the clusters could be gravitationally lensed, and we have identified a sample of potential cases of cluster-lensed Herschel sources that could be targeted in follow-up studies.

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arXiv2010

The Properties of the Interstellar Medium within a Star-Forming Galaxy at z=2.3

We present an analysis of the molecular and atomic gas emission in the rest-frame far-infrared and sub-millimetre, from the lensed z=2.3 sub-millimetre galaxy SMM J2135-0102. We obtain very high signal-to-noise detections of 11 transitions from 3 species and limits on a further 20 transitions from 9 species. We use the 12CO, [CI] and HCN line strengths to investigate the gas mass, kinematic structure and interstellar medium (ISM) chemistry, and find strong evidence for a two-phase medium comprising a hot, dense, luminous component and an underlying extended cool, low-excitation massive component. Employing photo-dissociation region models we show that on average the molecular gas is exposed to a UV radiation field that is ~1000 x more intense than the Milky Way, with star-forming regions having a characteristic density of n~10^4 /cm^3. These conditions are similar to those found in local ULIRGs and in the central regions of typical starburst galaxies, even though the star formation rate is far higher in this system. The 12CO spectral line energy distribution and line profiles give strong evidence that the system comprises multiple kinematic components with different conditions, including temperature, and line ratios suggestive of high cosmic ray flux within clouds. We show that, when integrated over the galaxy, the gas and star-formation surface densities appear to follow the Kennicutt-Schmidt relation, although when compared to high-resolution sub-mm imaging, our data suggest that this relation breaks down on scales of <100pc. By virtue of the lens amplification, these observations uncover a wealth of information on the star formation and ISM at z~2.3 at a level of detail that has only recently become possible at z<0.1, and show the potential physical properties that will be studied in unlensed galaxies when ALMA is in full operation. (Abridged).

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arXiv2010

LoCuSS: Probing Galaxy Transformation Physics with Herschel

We present an early broad-brush analysis of Herschel/PACS observations of star-forming galaxies in 8 galaxy clusters drawn from our survey of 30 clusters at z~0.2. We define a complete sample of 192 spectroscopically confirmed cluster members down to L_TIR>3x10^10L_sun and L_K>0.25L_sun. The average K-band and bolometric infrared luminosities of these galaxies both fade by a factor of ~2 from clustercentric radii of 2r_200 to ~0.5r_200, indicating that as galaxies enter the clusters ongoing star-formation stops first in the most massive galaxies, and that the specific star-formation rate (SSFR) is conserved. On smaller scales the average SSFR jumps by 25%, suggesting that in cluster cores processes including ram pressure stripping may trigger a final episode of star-formation that presumably exhausts the remaining gas. This picture is consistent with our comparison of the Herschel-detected cluster members with the cluster mass distributions, as measured in our previous weak-lensing study of these clusters. For example, the spatial distribution of the Herschel sources is positively correlated with the structures in the weak-lensing mass maps at 5sigma significance, with the strongest signal seen at intermediate group-like densities. The strong dependence of the total cluster IR luminosity on cluster mass L_TIR propto M_virial^2 is also consistent with accretion of galaxies and groups of galaxies (i.e. the substructure mass function) driving the cluster IR luminosity. The most surprising result is that roughly half of the Herschel-detected cluster members have redder S_100/S_24 flux ratios than expected, based on the Rieke et al. models. On average cluster members are redder than non-members, and the fraction of red galaxies increases towards the cluster centers, both of which indicate that these colors are not attributable to systematic photometric errors. [Abridged]

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arXiv2010

Herschel observations of FIR emission lines in brightest cluster galaxies

The question of how much gas cools in the cores of clusters of galaxies has been the focus of many, multiwavelength studies in the past 30 years. In this letter we present the first detections of the strongest atomic cooling lines, [C II], [O I] and [N I] in two strong cooling flow clusters, A1068 and A2597, using Herschel PACS. These spectra indicate that the substantial mass of cold molecular gas (>10^9 Mo) known to be present in these systems is being irradiated by intense UV radiation, most probably from young stars. The line widths of these FIR lines indicate that they share dynamics similar but not identical to other ionised and molecular gas traced by optical, near-infrared and CO lines. The relative brightness of the FIR lines compared to CO and FIR luminosity is consistent with other star-forming galaxies indicating that the properties of the molecular gas clouds in cluster cores and the stars they form are not unusual. These results provide additional evidence for a reservoir of cold gas that is fed by the cooling of gas in the cores of the most compact clusters and provide important diagnostics of the temperature and density of the dense clouds this gas resides in.

astro-ph.CO↗
arXiv2010

Herschel photometry of brightest cluster galaxies in cooling flow clusters

The dust destruction timescales in the cores of clusters of galaxies are relatively short given their high central gas densities. However, substantial mid-infrared and sub-mm emission has been detected in many brightest cluster galaxies. In this letter we present Herschel PACS and SPIRE photometry of the brightest cluster galaxy in three strong cooling flow clusters, A1068, A2597 and Zw3146. This photometry indicates that a substantial mass of cold dust is present (>3 x 10^7 Mo) at temperatures significantly lower (20-28K) than previously thought based on limited MIR and/or sub-mm results. The mass and temperature of the dust appear to match those of the cold gas traced by CO with a gas-to-dust ratio of 80-120.

astro-ph.CO↗
arXiv2010

Herschel and SCUBA-2 imaging and spectroscopy of a bright, lensed submillimetre galaxy at z = 2.3

We present a detailed analysis of the far-IR properties of the bright, lensed, z = 2.3, SMG, SMM J2135-0102, using new observations with Herschel, SCUBA-2 and the VLA. These data allow us to constrain the galaxy's SED and show that it has an intrinsic rest-frame 8-1000um luminosity, L(bol), of (2.3 +/- 0.2) x 10^12 L(sun) and a likely SFR of ~400 M(sun)/yr. The galaxy sits on the far-IR/radio correlation for far-IR-selected galaxies. At ~>70um, the SED can be described adequately by dust components with T(d) ~ 30 and 60K. Using SPIRE's Fourier Transform Spectrometer we report a detection of the [CII] 158um cooling line. If the [CII], CO and far-IR continuum arise in photo-dissociation regions, we derive a characteristic gas density, n ~ 10^3 cm^-3, and a far-UV radiation field, G_0, 10^3x stronger than the Milky Way. L([CII])/L(bol) is significantly higher than in local ULIRGs but similar to the values found in local star-forming galaxies and starburst nuclei. This is consistent with SMM J2135-0102 being powered by starburst clumps distributed across ~2 kpc, evidence that SMGs are not simply scaled-up ULIRGs. Our results show that SPIRE's FTS has the ability to measure the redshifts of distant, obscured galaxies via the blind detection of atomic cooling lines, but it will not be competitive with ground-based CO-line searches. It will, however, allow detailed study of the integrated properties of high-redshift galaxies, as well as the chemistry of their ISM, once more suitably bright candidates have been found.

astro-ph.CO↗
arXiv2010

The X-ray brightest clusters of galaxies from the Massive Cluster Survey

We present a statistically complete sample of very X-ray luminous galaxy clusters detected in the MAssive Cluster Survey (MACS). This second MACS release comprises all 34 MACS clusters with nominal X-ray fluxes in excess of 2x10^(-12) erg/s/cm^2 (0.1-2.4 keV) in the ROSAT Bright Source Catalogue; two thirds of them are new discoveries. Extending over the redshift range from 0.3 to 0.5, this subset complements the complete sample of the 12 most distant MACS clusters (z>0.5) published in 2007 and further exemplifies the efficacy of X-ray selection for the compilation of samples of intrinsically massive galaxy clusters. Extensive follow-up observations with Chandra/ACIS led to three additional MACS cluster candidates being eliminated as (predominantly) X-ray point sources. For another four clusters --- which, however, remain in our sample of 34 --- the point-source contamination was found to be about 50%. The median X-ray luminosity of 1.3x10^45 erg/s (0.1-2.4 keV, Chandra, within r_500) of the clusters in this subsample demonstrates the power of the MACS survey strategy to find the most extreme and rarest clusters out to significant redshift. A comparison of the optical and X-ray data for all clusters in this release finds a wide range of morphologies with no obvious bias in favour of either relaxed or merging systems.

astro-ph.CO↗
arXiv2010

Chandra observation of two shock fronts in the merging galaxy cluster Abell 2146

We present a new Chandra observation of the galaxy cluster Abell 2146 which has revealed a complex merging system with a gas structure that is remarkably similar to the Bullet cluster (eg. Markevitch et al. 2002). The X-ray image and temperature map show a cool 2-3 keV subcluster with a ram pressure stripped tail of gas just exiting the disrupted 6-7 keV primary cluster. From the sharp jump in the temperature and density of the gas, we determine that the subcluster is preceded by a bow shock with a Mach number M=2.2+/-0.8, corresponding to a velocity v=2200^{+1000}_{-900} km/s relative to the main cluster. We estimate that the subcluster passed through the primary core only 0.1-0.3 Gyr ago. In addition, we observe a slower upstream shock propagating through the outer region of the primary cluster and calculate a Mach number M=1.7+/-0.3. Based on the measured shock Mach numbers M~2 and the strength of the upstream shock, we argue that the mass ratio between the two merging clusters is between 3 and 4 to one. By comparing the Chandra observation with an archival HST observation, we find that a group of galaxies is located in front of the X-ray subcluster core but the brightest cluster galaxy is located immediately behind the X-ray peak.

astro-ph.CO↗
arXiv2010

MACSJ1423.8+2404: Gravitational Lensing by a Massive, Relaxed Cluster of Galaxies at z=0.54

We present results of a gravitational-lensing and optical study of MACS ,J1423.8+2404 (z=0.545, MACS, J1423). Our analysis uses high-resolution images taken with the Hubble Space Telescope in the F555W and F814W passbands, ground based imaging in eight optical and near-infrared filters obtained with Subaru and CFHT, as well as extensive spectroscopic data gathered with the Keck telescopes. At optical wavelengths the cluster exhibits no sign of substructure and is dominated by a cD galaxy that is 2.1 magnitudes (K-band) brighter than the second brightest cluster member, suggesting that MACS, J1423 is close to be fully virialized. Analysis of the redshift distribution of 140 cluster members reveals a Gaussian distribution, mildly disturbed by the presence of a loose galaxy group that may be falling into the cluster along the line of sight. Combining strong-lensing constraints from two spectroscopically confirmed multiple-image systems near the cluster core with a weak-lensing measurement of the gravitational shear on larger scales, we derive a parametric mass model for the mass distribution. All constraints can be satisfied by a uni-modal mass distribution centred on the cD galaxy and exhibiting very little substructure. The derived projected mass of M(<65\arcsec [415 kpc])=(4.3\pm0.6)\times 10^{14} M_sun is about 30% higher than the one derived from X-ray analyses assuming spherical symmetry, suggesting a slightly prolate mass distribution consistent with the optical indication of residual line-of-sight structure. The similarity in shape and excellent alignment of the centroids of the total mass, K-band light, and intra-cluster gas distributions add to the picture of a highly evolved system [ABRIDGED]

astro-ph.CO↗
arXiv2009

An AzTEC 1.1-mm Survey for ULIRGs in the field of the Galaxy Cluster MS 0451.6-0305

We have undertaken a deep (sigma~1.1 mJy) 1.1-mm survey of the z=0.54 cluster MS 0451.6-0305 using the AzTEC camera on the James Clerk Maxwell Telescope. We detect 36 sources with S/N>3.5 in the central 0.10 deg^2 and present the AzTEC map, catalogue and number counts. We identify counterparts to 18 sources (50%) using radio, mid-infrared, Spitzer IRAC and Submillimeter Array data. Optical, near- and mid-infrared spectral energy distributions are compiled for the 14 of these galaxies with detectable counterparts, which are expected to contain all likely cluster members. We then use photometric redshifts and colour selection to separate background galaxies from potential cluster members and test the reliability of this technique using archival observations of submillimetre galaxies. We find two potential MS 0451-03 members, which, if they are both cluster galaxies have a total star-formation rate (SFR) of ~100 solar masses per year -- a significant fraction of the combined SFR of all the other galaxies in MS 0451-03. We also examine the stacked rest-frame mid-infrared, millimetre and radio emission of cluster members below our AzTEC detection limit and find that the SFRs of mid-IR selected galaxies in the cluster and redshift-matched field populations are comparable. In contrast, the average SFR of the morphologically classified late-type cluster population is ~3 times less than the corresponding redshift-matched field galaxies. This suggests that these galaxies may be in the process of being transformed on the red-sequence by the cluster environment. Our survey demonstrates that although the environment of MS 0451-03 appears to suppress star-formation in late-type galaxies, it can support active, dust-obscured mid-IR galaxies and potentially millimetre-detected LIRGs.

astro-ph.CO↗
arXiv2009

The REFLEX galaxy cluster survey. VIII. Spectroscopic observations and optical atlas

We present the final data from the spectroscopic survey of the ROSAT-ESO Flux-Limited X-ray (REFLEX) catalog of galaxy clusters. The REFLEX survey covers 4.24 steradians (34% of the entire sky) below a declination of 2.5 deg and at high Galactic latitude (|b| > 20 deg). The REFLEX catalog includes 447 entries with a median redshift of 0.08 and is better than 90% complete to a limiting flux fx = 3x10^{-12} erg s^{-1} cm^{-2} (0.1 to 2.4 keV), representing the largest statistically homogeneous sample of clusters drawn from the ROSAT All-Sky Survey (RASS) to date. Here we describe the details of the spectroscopic observations carried out at the ESO 1.5 m, 2.2 m, and 3.6 m telescopes, as well as the data reduction and redshift measurement techniques. The spectra typically cover the wavelength range 3600-7500 A at a FWHM resolution of ~14 A, and the measured redshifts have a total rms error of ~100 km s^{-1}. In total we present 1406 new galaxy redshifts in 192 clusters, most of which previously did not have any redshift measured. Finally, the luminosity/redshift distributions of the cluster sample and a comparison to the no-evolution expectations from the cluster X-ray luminosity function are presented.

astro-ph.CO↗
arXiv2009

Integral field spectroscopy of ionized and molecular gas in cool cluster cores: evidence for cold feedback?

We present VLT-SINFONI K-band IFU spectroscopy of the central galaxies in the cool core clusters A1664, A2204 and PKS 0745-191, to probe the Pa-alpha and ro-vibrational H2 line emission. In A1664 the two emission-line velocity systems seen in our previous H-alpha data appear in both Pa-alpha and H2 emission, with notable morphological differences. The recession velocity of the red component of Pa-alpha increases linearly with decreasing radius, particularly along an 8 kpc filament aligned with the major axis of the underlying galaxy and the cluster X-ray emission. These kinematics are modelled as gravitational free-fall as gas cools rapidly out of the hot phase. In A2204 the gas shows 3 or 4 filaments reaching 10 kpc, three of which lie towards `ghost bubbles' seen in X-ray imaging. For PKS 0745-191, we confirm the twin-arm morphology of previous narrow-band images; the Pa-alpha kinematics suggest rotational motion about an axis aligned with the kpc-scale radio jet; on nucleus, we find a broad Pa-alpha component (FWHM 1700 km/s) and a secondary H2 system redshifted by +500 km/s. The H2 v=1-0 S(3)/Pa-alpha ratio is highest in isolated and extended regions where it matches the levels in the NGC 1275 filaments as modelled by Ferland et al. Regions with lower ratios highlight active star formation and are often kinematically quiescent (FWHM < 200 km/s). Our findings suggest that these clusters may be captured in different stages of the `cold feedback' cycle of Pizzolato & Soker, with A1664 in a brief phase of extreme cooling and star formation prior to an AGN heating event; PKS 0745-191 in outburst with the AGN accreting from a cool gas disk, and A2204 in a later phase where cool gas is dragged out of the galaxy by the buoyant rise of old radio bubbles (abridged).

astro-ph.GA↗
arXiv2009

A spectacular giant arc in the massive cluster lens MACSJ1206.2-0847

We discuss the X-ray and optical properties of the massive galaxy cluster MACSJ1206.2-0847 (z=0.4385), discovered in the Massive Cluster Survey (MACS). Our Chandra observation of the system yields a total X-ray luminosity of 2.4 x 10^45 erg/s (0.1-2.4 keV) and a global gas temperature of (11.6 +/- 0.7) keV, very high values typical of MACS clusters. In both optical and X-ray images MACSJ1206 appears close to relaxed in projection, with a pronounced X-ray peak at the location of the brightest cluster galaxy (BCG); we interpret this feature as the remnant of a cold core. A spectacular giant gravitational arc, 15" in length, bright (V~21) and unusually red (R-K=4.3), is seen 20" west of the BCG; we measure a redshift of z=1.036 for the lensed galaxy. From our HST image of the cluster we identify the giant arc and its counter image as a seven-fold imaged system. An excess of X-ray emission in the direction of the arc coincides with a mild galaxy overdensity and could be the remnant of a minor merger with a group of galaxies. We derive estimates of the total cluster mass as well as of the mass of the cluster core using X-ray, dynamical, and gravitational-lensing techniques. For the mass enclosed by the giant arc (r<119 kpc) our strong-lensing analysis based on HST imaging yields a very high value of 1.1 x 10^14 M_sun, inconsistent with the much lower X-ray estimate of 0.5 x 10^14 M_sun. Similarly, the virial estimate of 4 x 10^15 M_sun for the total cluster mass, derived from multi-object spectroscopy of 38 cluster members, is significantly higher than the corresponding X-ray estimate of 1.7 x 10^15 M_sun. We take the discrepant mass estimates to be indicative of substructure along the line of sight during an ongoing merger event, an interpretation that is supported by the system's very high velocity dispersion of 1580 km/s.

astro-ph.HE↗
arXiv2009

The evolution of the red sequence slope in massive galaxy clusters

We investigate the evolution of the optical and near-infrared colour-magnitude relation in an homogeneous sample of massive clusters from z = 1 to the present epoch. By comparing deep Hubble Space Telescope ACS imaging of X-ray selected MACS survey clusters at z = 0.5 to the similarly selected LARCS sample at z = 0.1 we find that the rest-frame d(U -V)/dV slope of the colour-magnitude relation evolves with redshift which we attribute to the build up of the red sequence over time. This rest frame slope evolution is not adequately reproduced by that predicted from semi-analytic models based on the Millennium Simulation despite a prescription for the build up of the red sequence by in-falling galaxies, 'strangulation'. We observe no strong correlation between this slope and the cluster environment at a given redshift demonstrating that the observed evolution is not due to a secondary correlation. Also presented are near-infrared UKIRT WFCAM observations of the LARCS clusters which confirm and improve on the the result from Stott et al. (2007) finding that there has been a two-fold increase in faint MV > -20 galaxies on the red sequence since z = 0.5 to a significance of 5sigma.

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