Melanie Gendre
Researcher in Astrophysics (2006-2013)
&
Physics Teacher


Email: mgendre.at.gmail.com


Publications

♦ The relation between morphology, accretion modes and environmental factors in local radio AGN (2013)
Gendre, Best, Wall & Ker, 2013, MNRAS

The goal of this work is to determine the nature of the relation between morphology and accretion mode in radio galaxies, including environmental parameters. The CoNFIG extended catalogue (improved by new Ks-band identifications and estimated redshifts from UKIDSS, and spectral index measurements from new GMRT observations) is used to select a sub-sample of 206 radio galaxies with z<0.3 over a wide range of radio luminosity, which are morphology-classified using the Fanaroff-Riley (FR) classification of extended radio sources. For each galaxy, spectroscopic data are retrieved to determine the high/low excitation status of the source, related to its accretion mode. Environmental factors, such as the host galaxy luminosity and a richness factor are also computed, generally using SDSS data.


♦ Flux density variations of radio sources in M82 (2013)
Gendre, Fenech, Beswick, Muxlow & Argo, 2013, MNRAS

This paper presents the results of the 2009-2010 monitoring sessions of the starburst galaxy M82, obtained with the Multi-Element Radio-Linked Interferometer Network (MERLIN) at 5 GHz and e-MERLIN at 6 GHz. Combining several 5 GHz MERLIN epochs to form a map with 33.0 μJy bm-1 noise level, 52 discrete sources, mostly supernova remnants and HII regions, are identified. These include three objects which were not detected in the 2002 5 GHz MERLIN monitoring session: supernova SN2008iz, the transient source 43.78+59.3, and a new supernova remnant shell. Flux density variations, in the long (1981 to 2010), medium (2002 to 2010) and short (2009 to 2010) term are investigated. We find that flux densities of supernova remnants (SNRs) in M82 stay constant in most of the sample (∼95 per cent), although the distributions of flux density variations show an offset from zero. This is consistent with a slight statistical reduction in flux density of the source distribution. In addition, aside from SN2008iz and the well-known variable source 41.95+57.5, two sources display tentative evidence for short- and medium-term variations over the period 2009-2010. These sources are amongst the most compact SNR in M82. These flux density variations could be due to changes in the circumstellar and interstellar medium in which the shocks travel.


♦ Resolving the masers in M82 (2013)
Argo, Beswick, Muxlow, Fenech, van Langevelde, Gendre & Pedlar, 2013

Despite first being detected in the 1970s, surprisingly little is known about the OH main line maser population in the nearby starburst galaxy M82. Sometimes referred to as 'kilomasers', they have isotropic luminosities intermediate between Galactic masers and those found in more distant megamasers. Several observations have been carried by this group over the last ten years in an attempt to get a better handle on their nature. High velocity resolution VLA observations in 2006 showed that almost all of the maser spots, distributed across the central arcminute of the galaxy, were apparently coincident with background continuum features, and a handful displayed multiple velocity components. The majority of those with velocity structure are located on a blue-shifted arc in the pv-plane, spatially located on an arc northward of the peculiar source known as B41.95+57.5. Now, new results from high spatial and spectral resolution observations with the EVN have resolved several of these masers into multiple spatial components for the first time. The maser emission is compared with known continuum sources in the galaxy, and we conclude that at least some of the maser emission is from high-gain maser action.


♦ New insights on the z-α correlation from complete radio samples (2012)
Ker, Best, Rigby, Röttgering & Gendre. 2012, MNRAS

The existence of a correlation between observed radio spectral index (alpha) and redshift (z) has long been used as a method for locating high-z radio galaxies. We use 9 highly spectroscopically complete radio samples, selected at different frequencies and flux limits, to determine the efficiency of this method, and compare consistently observed correlations between alpha, luminosity, linear size, and redshift. We observe a weak correlation between z and alpha which remains even when Malmquist bias is removed. The strength of this correlation depends on both the k-correction and sample selection frequency, in addition to the frequency at which alpha is measured, and consistent results for both high and low frequency selected samples are only seen if analysis is restricted to just extended radio galaxies. Many of the highest redshift radio galaxies are very compact and often display a negatively curved or peaked spectrum, and therefore the low-frequency radio spectrum as a whole should be studied; this is something for which the LOFAR will be crucial. We quantify both the efficiency and the completeness of various techniques used to select high-z radio galaxies. A steep-spectrum cut applied to low-frequency selected samples can more than double the fraction of high-z sources, but at a cost of excluding over half of the high-z sources present in the original sample. An angular size cut is an almost as equally effective method as a steep-spectrum cut, and works for both high and low frequency selected samples. In multi-wavelength data, selection first of infrared-faint radio sources remains by far the most efficient method of selecting high-z sources. We present a simple method for selecting high-z radio galaxies, based purely on combining their radio properties of alpha and angular size, with the addition of the K-band magnitude if available.


♦ Space Densities of AGN and the FR Dichotomy (2010)
Ph.D. Thesis, Melanie Gendre, UBC, 2010

Extended double-lobe radio sources can be morphologically classified into two groups: Fanaroff-Riley (FR) type I sources have the highest surface brightness along the jets near the core and FR type II sources show the highest surface brightness at the lobe extremities, as well as more collimated jets. This thesis work focuses on a comparison of the space densities of FRI and FRII sources at different epochs, with a particular focus on FRI sources. First, we present the construction of the Combined NVSS-FIRST Galaxy catalogue (CoNFIG), a new sample of radio sources at 1.4 GHz. It includes VLA observations, FRI/FRII morphology classifications, optical identifications and redshift estimates. The final catalogue consists of 858 sources over 4 samples (CoNFIG-1, 2, 3 and 4 with flux density limits of S1.4GHz =1.3, 0.8, 0.2 and 0.05 Jy respectively). It is 95.7% complete in radio morphology classification and 74.3% of the sources have redshift data. Combining CoNFIG with complementary samples, the distribution and cosmic evolution of FRI and FRII sources are investigated. We find that FRI sources undergo mild evolution and that, at the same radio luminosity, FRI and FRII sources show similar space density enhancements in various redshift ranges, implying a common mechanism powering the luminosity-dependent evolution. This improved understanding of radio galaxy evolution will also give better insight into the the physics of AGN and their role in galaxy formation.


♦ The CoNFIG Catalogue - II. Comparison of Space Densities in the FR Dichotomy (2010)
Gendre, Best & Wall, 2010, MNRAS

This paper focuses on a comparison of the space densities of FRI and FRII sources at different epochs, with a particular focus on FRI sources. First, we present the concluding steps in constructing the Combined NVSS-FIRST Galaxy catalogue (CoNFIG), including new VLA observations, optical identifications and redshift estimates. The final catalogue consists of 859 sources over 4 samples (CoNFIG-1, 2, 3 and 4 with flux density limits of S1.4GHz = 1.3, 0.8, 0.2 and 0.05 Jy respectively). It is 95.7% complete in radio morphology classification and 74.3% of the sources have redshift data. Combining CoNFIG with complementary samples, the distribution and evolution of FRI and FRII sources are investigated. We find that FRI sources undergo mild evolution and that, at the same radio luminosity, FRI and FRII sources show similar space density enhancements in various redshift ranges, possibly implying a common evolution.


♦ IAU S267: The Combined NVSS-FIRST Galaxy (CoNFIG) Catalogue: Evolution of AGN Space Densities and the FR Dichotomy (2009)
IAU S267 Proceedings
Poster

We focus on a comparison of the space densities of FRI and FRII sources at different epochs, and find that FRI and FRII sources show similar space density enhancements in various redshift ranges, possibly implying a common evolution.


♦ IAU SpS4: Exploring the Solar System with a Human Orrery (2009)
Poster

Astronomy and physics education research shows, again and again, that interactive instruction increases student learning. This is particularly important when dealing with introductory courses. The UBC Physics and Astronomy course Exploring the Solar System is a survey course in astronomy offered to 200-250 third-year non-Science undergraduates each Term. Students attend three 1-hour lectures each week and, in smaller groups of 40, participate in a 50-minute, hands-on tutorial every 2nd week. For one of these tutorials, we designed an interactive, engaging activity adapted from an exhibit at the Armagh Observatory (Ireland), in which the students build and explore a working, scale model of the Solar System (an orrery), which shows the motion of the planets around the Sun. In the human orrery, students play the roles of the planets.


♦ The Combined NVSS-FIRST Galaxies (CoNFIG) Sample - I. Sample Definition, Classification and Evolution (2009)
Gendre & Wall, 2009, MNRAS
Erratum

The CoNFIG (Combined NVSS-FIRST Galaxies) sample is a new sample of 274 bright radio sources at 1.4 GHz. It was defined by selecting all sources with S1.4GHz≥ 1.3 Jy from the NRAO-VLA Sky Survey (NVSS) in the North field of the Faint Images of the Radio Sky at Twenty-cm (FIRST) survey. New radio observations obtained with the VLA for 31 of the sources are presented. The sample has complete FRI/FRII morphology identification; optical identifications and redshifts are available for 80% and 89% of the sample respectively, yielding a mean redshift of ~0.71. One of the goals of this survey is to get better definitions of luminosity distributions and source counts of FRI/FRII sources separately, in order to determine the evolution of the luminosity function for each type of source. We present a preliminary analysis, showing that these data are an important step towards examining various evolutionary schemes for these objects and to confirm or correct the dual population unified scheme for radio AGN. Improving our understanding of radio galaxy evolution will give better insight into the role of AGN feedback in galaxy formation.


♦ MRU Proceedings: The CENSORS Bright Sample of Radio AGN (2007)
2008, P.o.S. , MRU 97

The Combined NVSS-FIRST Galaxy (CoNFIG) survey was defined by selecting all sources with S1.4GHz≥1.3 Jy from the NRAO VLA Sky Survey (NVSS) in the north field of the Faint Images of the Radio Sky at Twenty-cm (FIRST) survey. We carried out FRI/FRII morphology classification from NVSS and FIRST survey data; to complete this process, new 8GHz VLA observations for 31 sources were obtained at 0.24 arcsec resolution. Optical identifications and redshift information were compiled for about 80% of the 270 radio sources in the sample, the mean redshift being ~0.6. A major goal of this sample is a better definition of the individual luminosity distributions and source counts for FRI and FRII sources, in order to determine accurately the evolution of the luminosity function for both types. Amongst the aims are the issues of whether the two populations are really distinct, whether physical evolution schemes permit one type to evolve into the other, whether the dual-population unified scheme for radio AGN remains viable, and the role radio AGN - star-formation feedback mechanisms.