arXiv subjects

Malcolm Bremer

Publications and source records attributed to Malcolm Bremer.

27 records · Page 2Linked to original sources

arXiv2016

Galaxy And Mass Assembly (GAMA): $\mathcal{M_\star}-R_{\rm e}$ relations of $z=0$ bulges, discs and spheroids

We perform automated bulge + disc decomposition on a sample of $\sim$7500 galaxies from the Galaxy And Mass Assembly (GAMA) survey in the redshift range of 0.002$<$z$<$0.06 using SIGMA, a wrapper around GALFIT3. To achieve robust profile measurements we use a novel approach of repeatedly fitting the galaxies, varying the input parameters to sample a large fraction of the input parameter space. Using this method we reduce the catastrophic failure rate significantly and verify the confidence in the fit independently of $χ^2$. Additionally, using the median of the final fitting values and the 16$^{th}$ and 84$^{th}$ percentile produces more realistic error estimates than those provided by GALFIT, which are known to be underestimated. We use the results of our decompositions to analyse the stellar mass - half-light radius relations of bulges, discs and spheroids. We further investigate the association of components with a parent disc or elliptical relation to provide definite $z=0$ disc and spheroid $\mathcal{M_\star}-R_{\rm e}$ relations. We conclude by comparing our local disc and spheroid $\mathcal{M_\star}-R_{\rm e}$ to simulated data from EAGLE and high redshift data from CANDELS-UDS. We show the potential of using the mass-size relation to study galaxy evolution in both cases but caution that for a fair comparison all data sets need to be processed and analysed in the same manner.

astro-ph.GA↗

arXiv2016

Morphological evolution of cluster red sequence galaxies in the past 9 Gyr

Galaxies arrive on the red sequences of clusters at high redshift ($z>1$) once their star formation is quenched and evolve passively thereafter. However, we have previously found that cluster red sequence galaxies (CRSGs) undergo significant morphological evolution subsequent to the cessation of star formation, at some point in the past 9-10~Gyr. Through a detailed study of a large sample of cluster red sequence galaxies spanning $0.2<z<1.4$ we elucidate the details of this evolution. Below $z \sim 0.5-0.6$ (in the last 5-6 Gyr) there is little or no morphological evolution in the population as a whole, unlike in the previous 4-5 Gyrs. Over this earlier time (i) disk-like systems with S{é}rsic $n < 2$ progressively disappear, as (ii) the range of their axial ratios similarly decreases, removing the most elongated systems (those consistent with thin disks seen at an appreciable inclination angle), and (iii) radial colour gradients (bluer outwards) decrease in an absolute sense from significant age-related gradients to a residual level consistent with the metallicity-induced gradients seen in low redshift cluster members. The distribution of their effective radii shows some evidence of evolution, consistent with growth of {\it at most} a factor $<1.5$ between $z\sim 1.4$ and $z \sim 0.5$, significantly less than for comparable field galaxies, while the distribution of their central ($<1$kpc) bulge surface densities shows no evolution at least at $z<1$. A simple model involving the fading and thickening of a disk component after comparatively recent quenching (after $z\sim 1.5$) around an otherwise passively evolving older spheroid component is consistent with all of these findings.

astro-ph.GA↗

arXiv2016

Galaxy And Mass Assembly (GAMA): Understanding the wavelength dependence of galaxy structure with bulge-disc decompositions

With a large sample of bright, low-redshift galaxies with optical$-$near-IR imaging from the GAMA survey we use bulge-disc decompositions to understand the wavelength-dependent behavior of single-Sérsic structural measurements. We denote the variation in single-Sérsic index with wavelength as $\mathcal{N}$, likewise for effective radius we use $\mathcal{R}$. We find that most galaxies with a substantial disc, even those with no discernable bulge, display a high value of $\mathcal{N}$. The increase in Sérsic index to longer wavelengths is therefore intrinsic to discs, apparently resulting from radial variations in stellar population and/or dust reddening. Similarly, low values of $\mathcal{R}$ ($<$ 1) are found to be ubiquitous, implying an element of universality in galaxy colour gradients. We also study how bulge and disc colour distributions vary with galaxy type. We find that, rather than all bulges being red and all discs being blue in absolute terms, both components become redder for galaxies with redder total colours. We even observe that bulges in bluer galaxies are typically bluer than discs in red galaxies, and that bulges and discs are closer in colour for fainter galaxies. Trends in total colour are therefore not solely due to the colour or flux dominance of the bulge or disc.

astro-ph.GA↗

arXiv2014

The XXL Survey V: Detection of the Sunyaev-Zel'dovich effect of the Redshift 1.9 Galaxy Cluster XLSSU J021744.1-034536 with CARMA

We report the detection of the Sunyaev-Zel'dovich (SZ) effect of galaxy cluster XLSSU J021744.1-034536, using 30 GHz CARMA data. This cluster was discovered via its extended X-ray emission in the XMM-Newton Large Scale Structure survey, the precursor to the XXL survey. It has a photometrically determined redshift $z=1.91^{+0.19}_{-0.21}$, making it among the most distant clusters known, and nominally the most distant for which the SZ effect has been measured. The spherically integrated Comptonization is $Y_{500}=(3.0\pm0.4)\times 10^{-12}$, a measurement which is relatively insensitive to assumptions regarding the size and redshift of the cluster, as well as the background cosmology. Using a variety of locally calibrated cluster scaling relations extrapolated to z~2, we estimate a mass $M_{500} \sim (1$-$2)\times 10^{14}M_{sun}$ from the X-ray flux and SZ signal. The measured properties of this cluster are in good agreement with the extrapolation of an X-ray luminosity-SZ effect scaling relation calibrated from clusters discovered by the South Pole Telescope at higher masses and lower redshifts. The full XXL-CARMA sample will provide a more complete, multi-wavelength census of distant clusters in order to robustly extend the calibration of cluster scaling relations to these high redshifts.

astro-ph.CO↗

arXiv2012

Future Science Prospects for AMI

The Arcminute Microkelvin Imager (AMI) is a telescope specifically designed for high sensitivity measurements of low-surface-brightness features at cm-wavelength and has unique, important capabilities. It consists of two interferometer arrays operating over 13.5-18 GHz that image structures on scales of 0.5-10 arcmin with very low systematics. The Small Array (AMI-SA; ten 3.7-m antennas) couples very well to Sunyaev-Zel'dovich features from galaxy clusters and to many Galactic features. The Large Array (AMI-LA; eight 13-m antennas) has a collecting area ten times that of the AMI-SA and longer baselines, crucially allowing the removal of the effects of confusing radio point sources from regions of low surface-brightness, extended emission. Moreover AMI provides fast, deep object surveying and allows monitoring of large numbers of objects. In this White Paper we review the new science - both Galactic and extragalactic - already achieved with AMI and outline the prospects for much more.

astro-ph.IM↗

arXiv2008

First-Year Spectroscopy for the SDSS-II Supernova Survey

This paper presents spectroscopy of supernovae discovered in the first season of the Sloan Digital Sky Survey-II Supernova Survey. This program searches for and measures multi-band light curves of supernovae in the redshift range z = 0.05 - 0.4, complementing existing surveys at lower and higher redshifts. Our goal is to better characterize the supernova population, with a particular focus on SNe Ia, improving their utility as cosmological distance indicators and as probes of dark energy. Our supernova spectroscopy program features rapid-response observations using telescopes of a range of apertures, and provides confirmation of the supernova and host-galaxy types as well as precise redshifts. We describe here the target identification and prioritization, data reduction, redshift measurement, and classification of 129 SNe Ia, 16 spectroscopically probable SNe Ia, 7 SNe Ib/c, and 11 SNe II from the first season. We also describe our efforts to measure and remove the substantial host galaxy contamination existing in the majority of our SN spectra.

astro-ph↗

arXiv2007

On Contamination and Completeness in z>5 Lyman Break Galaxy Surveys

A large population of z>5 Lyman break galaxies has been identified in recent years. However, the high redshift galaxies selected by different surveys are subject to a variety of selection effects - some overt, others more subtle. We present an analysis of sample completeness and contamination issues in high redshift surveys, focusing on surveys at z=5 and using a spectroscopically-confirmed low redshift sample from the DEEP2 survey in order to characterise contaminant galaxies. We find that most surveys underestimate their contamination from highly clustered galaxies at z=1 and stars. We consider the consequences of this for both the rest-frame ultraviolet luminosity function and the clustering signal from z=5 galaxies. We also find that sources with moderate strength Lyman-alpha emission lines can be omitted from dropout surveys due to their blue colours, again effecting the derived luminosity functions. We discuss the points of comparison between different samples, and the applicability of survey-specific results to the population at z>5 in general.

astro-ph↗

arXiv2003

Luminous Lyman Break Galaxies at z>5 and the Source of Reionization

We have discovered six galaxies with spectroscopically confirmed redshifts of 4.8 1.5 in the field, this photometric cut designed to select galaxies at z>4.8. The line fluxes range between 0.2 to 2.5 x 10^-17 ergs cm^-2 s^-1 indicating luminosities of around 10^42-43 ergs s^-1 for Ly-alpha and their high emission line equivalent widths suggest very young ages (<10^8 yrs). A further line-emitting object with no detectable continuum was serendipitously detected by spectroscopy. If this line is Ly-alpha then it is from a source at z=6.6, making this the most distant galaxy known. However, the redshift cannot be considered secure as it is based on a single line. No broad emission line objects (quasars) were detected. The 13 sources at I_AB<26.2 are less than that expected if the luminosity function of dropout galaxies remained unchanged between z=3 and z=6, although the deficit is not highly significant given possible cosmic variance. The UV luminosity density from galaxies brighter than our flux limit is considerably less than that necessary to keep the volume probed by our field at ~5.3 ionized. These galaxies are observed within several hundred Myr of the end of the epoch of reionization (z=6-7), with little time for the luminosity function to evolve. This, and the lack of detected quasars, imply that the bulk of the UV flux that reionized the universe came from faint galaxies with M_(1700 ang)>-21.

astro-ph↗

arXiv2000

On the evolution of young radio-loud AGN

This paper describes an investigation of the early evolution of extragalactic radio sources using samples of faint and bright Gigahertz Peaked Spectrum (GPS) and Compact Steep Spectrum (CSS) radio galaxies. Correlations found between their peak frequency, peak flux density and angular size provide strong evidence that synchrotron self absorption is the cause of the spectral turnovers, and indicate that young radio sources evolve in a self-similar way. In addition, the data seem to suggest that the sources are in equipartition while they evolve. If GPS sources evolve to large size radio sources, their redshift dependent birth-functions should be the same. Therefore, since the lifetimes of radio sources are thought to be short compared to the Hubble time, the observed difference in redshift distribution between GPS and large size sources must be due to a difference in slope of their luminosity functions. We argue that this slope is strongly affected by the luminosity evolution of the individual sources. A scenario for the luminosity evolution is proposed in which GPS sources increase in luminosity and large scale radio sources decrease in luminosity with time. This evolution scenario is expected for a ram-pressure confined radio source in a surrounding medium with a King profile density. In the inner parts of the King profile, the density of the medium is constant and the radio source builds up its luminosity, but after it grows large enough the density of th e surrounding medium declines and the luminosity of the radio source decreases. A comparison of the local luminosity function (LLF) of GPS galaxies with that of extended sources is a good test for this evolution scenario [abridged].

astro-ph↗