arXiv subjects

Pauline Barmby

Publications and source records attributed to Pauline Barmby.

At least 37 records · Page 2Linked to original sources

arXiv2019

LRP2020: Astrostatistics in Canada

(Abridged from Executive Summary) This white paper focuses on the interdisciplinary fields of astrostatistics and astroinformatics, in which modern statistical and computational methods are applied to and developed for astronomical data. Astrostatistics and astroinformatics have grown dramatically in the past ten years, with international organizations, societies, conferences, workshops, and summer schools becoming the norm. Canada's formal role in astrostatistics and astroinformatics has been relatively limited, but there is a great opportunity and necessity for growth in this area. We conducted a survey of astronomers in Canada to gain information on the training mechanisms through which we learn statistical methods and to identify areas for improvement. In general, the results of our survey indicate that while astronomers see statistical methods as critically important for their research, they lack focused training in this area and wish they had received more formal training during all stages of education and professional development. These findings inform our recommendations for the LRP2020 on how to increase interdisciplinary connections between astronomy and statistics at the institutional, national, and international levels over the next ten years. We recommend specific, actionable ways to increase these connections, and discuss how interdisciplinary work can benefit not only research but also astronomy's role in training Highly Qualified Personnel (HQP) in Canada.

astro-ph.IM↗

arXiv2019

Dust properties and star formation of approximately a thousand local galaxies

[ABRIDGED] We derive the dust properties for 753 local galaxies and examine how these relate to some of their physical properties. We model their global dust-SEDs, treated statistically as an ensemble within a hierarchical Bayesian dust-SED modeling approach. The model-derived properties are the dust masses (Mdust), the average interstellar radiation field intensities (Uav), the mass fraction of very small dust grains ('QPAH' fraction), as well as their standard deviations. In addition, we use mid-IR observations to derive SFR and Mstar, quantities independent of the modeling. We derive distribution functions of the properties for the galaxy ensemble and per galaxy type. The mean value of Mdust for the ETGs is lower than that for the LTGs and IRs, despite ETGs and LTGs having Mstar spanning across the whole range observed. The Uav and 'QPAH' fraction show no difference among different galaxy types. When fixing Uav to the Galactic value, the derived 'QPAH' fraction varies across the Galactic value (0.071). The sSFR increases with galaxy type, while this is not the case for the dust-sSFR (=SFR/Mdust), showing an almost constant SFE per galaxy type. The galaxy sample is characterised by a tight relation between Mdust and Mstar for the LTGs and Irs, while ETGs scatter around this relation and tend towards smaller Mdust. While the relation indicates that Mdust may fundamentally be linked to Mstar, metallicity and Uav are the second parameter driving the scatter, which we investigate in a forthcoming work. We use the extended KS law to estimate Mgas and the GDR. The Mgas derived from the extended KS law is on average ~20% higher than that derived from the KS law, and a large standard deviation indicates the importance of the average SF present to regulate star formation and gas supply. The average GDR for the LTGs and IRs is 370, while including the ETGs gives an average of 550. [ABRIDGED]

astro-ph.GA↗

arXiv2018

The large-scale structure of the halo of the Andromeda galaxy II. Hierarchical structure in the Pan-Andromeda Archaeological Survey

The Pan-Andromeda Archaeological Survey is a survey of $>400$ square degrees centered on the Andromeda (M31) and Triangulum (M33) galaxies that has provided the most extensive panorama of a $L_\star$ galaxy group to large projected galactocentric radii. Here, we collate and summarise the current status of our knowledge of the substructures in the stellar halo of M31, and discuss connections between these features. We estimate that the 13 most distinctive substructures were produced by at least 5 different accretion events, all in the last 3 or 4 Gyrs. We suggest that a few of the substructures furthest from M31 may be shells from a single accretion event. We calculate the luminosities of some prominent substructures for which previous estimates were not available, and we estimate the stellar mass budget of the outer halo of M31. We revisit the problem of quantifying the properties of a highly structured dataset; specifically, we use the OPTICS clustering algorithm to quantify the hierarchical structure of M31's stellar halo, and identify three new faint structures. M31's halo, in projection, appears to be dominated by two `mega-structures', that can be considered as the two most significant branches of a merger tree produced by breaking M31's stellar halo into smaller and smaller structures based on the stellar spatial clustering. We conclude that OPTICS is a powerful algorithm that could be used in any astronomical application involving the hierarchical clustering of points. The publication of this article coincides with the public release of all PAndAS data products.

astro-ph.GA↗

arXiv2018

JINGLE, a JCMT legacy survey of dust and gas for galaxy evolution studies: I. Survey overview and first results

JINGLE is a new JCMT legacy survey designed to systematically study the cold interstellar medium of galaxies in the local Universe. As part of the survey we perform 850um continuum measurements with SCUBA-2 for a representative sample of 193 Herschel-selected galaxies with M*>10^9Msun, as well as integrated CO(2-1) line fluxes with RxA3m for a subset of 90 of these galaxies. The sample is selected from fields covered by the Herschel-ATLAS survey that are also targeted by the MaNGA optical integral-field spectroscopic survey. The new JCMT observations combined with the multi-wavelength ancillary data will allow for the robust characterization of the properties of dust in the nearby Universe, and the benchmarking of scaling relations between dust, gas, and global galaxy properties. In this paper we give an overview of the survey objectives and details about the sample selection and JCMT observations, present a consistent 30 band UV-to-FIR photometric catalog with derived properties, and introduce the JINGLE Main Data Release (MDR). Science highlights include the non-linearity of the relation between 850um luminosity and CO line luminosity, and the serendipitous discovery of candidate z>6 galaxies.

astro-ph.GA↗

arXiv2017

Milky Way Globular Cluster Metallicity and Low-Mass X-ray Binaries: The Red Giant Influence

Galactic and extragalactic studies have shown that metal-rich globular clusters (GCs) are approximately three times more likely to host bright low-mass X-ray binaries (LMXBs) than metal-poor GCs. There is no satisfactory explanation for this metallicity effect. We tested the hypothesis that the number density of red giant branch (RGB) stars is larger in metal-rich GCs, and thus potentially the cause of the metallicity effect. Using Hubble Space Telescope photometry for 109 unique Milky Way GCs, we investigated whether RGB star density was correlated with GC metallicity. Isochrone fitting was used to calculate the number of RGB stars, which were normalized by the GC mass and fraction of observed GC luminosity, and determined density using the volume at the half-light radius $r_{h}$. The RGB star number density was weakly correlated with metallicity [Fe/H], giving Spearman and Kendall Rank test $p$-values of 0.00016 and 0.00021 and coefficients $r_{s} = 0.35$ and $τ= 0.24$ respectively. This correlation may be biased by a possible dependence of $r_{h}$ on [Fe/H], although studies have shown that $r_{h}$ is correlated with Galactocentric distance and independent of [Fe/H]. The dynamical origin of the $r_{h}$-metallicity correlation (tidal stripping) suggests that metal-rich GCs may have had more active dynamical histories, which would promote LMXB formation. No correlation between the RGB star number density and metallicity was found when using only the GCs that hosted quiescent LMXBs. A complete census of quiescent LMXBs in our Galaxy is needed to further probe the metallicity effect, which will be possible with the upcoming launch of eROSITA.

astro-ph.GA↗

arXiv2016

The extended disc and halo of the Andromeda galaxy observed with Spitzer-IRAC

We present the first results from an extended survey of the Andromeda galaxy (M31) using 41.1 h of observations by Spitzer-IRAC at 3.6 and 4.5$\,μ$m. This survey extends previous observations to the outer disc and halo, covering total lengths of 4$.\!\!^\circ$4 and 6$.\!\!^\circ$6 along the minor and major axes, respectively. We have produced surface brightness profiles by combining the integrated light from background-corrected maps with stellar counts from a new catalogue of point sources. Using auxiliary catalogues we have carried out a statistical analysis in colour-magnitude space to discriminate M31 objects from foreground Milky Way stars and background galaxies. The catalogue includes 426,529 sources, of which 66 per cent have been assigned probability values to identify M31 objects with magnitude depths of [3.6]$\,=\,$19.0$\,\pm\,$0.2, [4.5]$\,=\,$18.7$\,\pm\,$0.2. We discuss applications of our data for constraining the stellar mass and characterising point sources in the outer radii.

astro-ph.GA↗

arXiv2016

The dustier early-type galaxies deviate from late-type galaxies' scaling relations

Several dedicated surveys focusing on early-type galaxies (ETGs) reveal that significant fractions of them are detectable in all interstellar medium phases studied to date. We select ETGs from the Herschel Reference Survey that have both far-infrared Herschel and either HI or CO detection (or both). We derive their star formation rates (SFR), stellar masses and dust masses via modelling their spectral energy distributions. We combine these with literature information on their atomic and molecular gas properties, in order to relate their star formation, total gas mass and dust mass on global scales. The ETGs deviate from the dust mass-SFR relation and the Schmidt-Kennicutt relation that SDSS star forming galaxies define: compared to SDSS galaxies, ETGs have more dust at the same SFR, or less SFR at the same dust mass. When placing them in the M*-SFR plane, ETGs show a much lower specific SFR as compared to normal star-forming galaxies. ETGs show a large scatter compared to the Schmidt-Kennicutt relation found locally within our Galaxy, extending to lower SFRs and gas mass surface densities. Using an ETG's SFR and the Schmidt-Kennicutt law to predict its gas mass leads to an underestimate. ETGs have similar observed-gas-to-modelled-dust mass ratios to star forming-galaxies of the same stellar mass, as well as they exhibit a similar scatter.

astro-ph.GA↗

arXiv2015

Star formation laws in the Andromeda galaxy: gas, stars, metals and the surface density of star formation

We use hierarchical Bayesian regression analysis to investigate star formation laws in the Andromeda galaxy (M31) in both local (30, 155, and 750pc) and global cases. We study and compare the well-known Kennicutt-Schmidt law, the extended Schmidt law and the metallicity/star formation correlation. Using a combination of H$α$ and 24 $μ$m emission, a combination of far-ultraviolet and 24$μ$m, and the total infrared emission, we estimate the total star formation rate (SFR) in M31 to be between $0.35\pm 0.04$M$_{\odot}$yr$^{-1}$ and $0.4\pm 0.04$M$_{\odot}$yr$^{-1}$. We produce a stellar mass surface density map using IRAC 3.6$μ$m emission and measured the total stellar mass to be $6.9 \times 10^{10}$M$_{\odot}$. For the Kennicutt-Schmidt law in M31, we find the power-law index $N$ to be between 0.49 and 1.18, for all the laws, the power-law index varies more with changing gas tracer than with SFR tracer. The power-law index also changes with distance from the centre of the galaxy. We also applied the commonly-used ordinary least squares fitting method and showed that using different fitting methods leads to different power-law indices. There is a correlation between the surface density of SFR and the stellar mass surface density, which confirms that the Kennicutt-Schmidt law needs to be extended to consider the other physical properties of galaxies. We found a weak correlation between metallicity, the SFR and the stellar mass surface density.

astro-ph.GA↗

arXiv2014

An Infrared Census of DUST in Nearby Galaxies with Spitzer (DUSTiNGS), I. Overview

Nearby resolved dwarf galaxies provide excellent opportunities for studying the dust-producing late stages of stellar evolution over a wide range of metallicity (-2.7 < [Fe/H] < -1.0). Here, we describe DUSTiNGS (DUST in Nearby Galaxies with Spitzer): a 3.6 and 4.5 micron post-cryogen Spitzer Space Telescope imaging survey of 50 dwarf galaxies within 1.5 Mpc that is designed to identify dust-producing Asymptotic Giant Branch (AGB) stars and massive stars. The survey includes 37 dwarf spheroidal, 8 dwarf irregular, and 5 transition-type galaxies. This near-complete sample allows for the building of statistics on these rare phases of stellar evolution over the full metallicity range. The photometry is >75% complete at the tip of the Red Giant Branch for all targeted galaxies, with the exception of the crowded inner regions of IC 10, NGC 185, and NGC 147. This photometric depth ensures that the majority of the dust-producing stars, including the thermally-pulsing AGB stars, are detected in each galaxy. The images map each galaxy to at least twice the half-light radius to ensure that the entire evolved star population is included and to facilitate the statistical subtraction of background and foreground contamination, which is severe at these wavelengths. In this overview, we describe the survey, the data products, and preliminary results. We show evidence for the presence of dust-producing AGB stars in 8 of the targeted galaxies, with metallicities as low as [Fe/H] = -1.9, suggesting that dust production occurs even at low metallicity.

astro-ph.GA↗

arXiv2014

Probing the interstellar medium of NGC1569 with Herschel

NGC1569 has some of the most vigorous star formation among nearby galaxies. It hosts two super star clusters (SSCs) and has a higher star formation rate (SFR) per unit area than other starburst dwarf galaxies. Extended emission beyond the galaxy's optical body is observed in warm and hot ionised and atomic hydrogen gas; a cavity surrounds the SSCs. We aim to understand the impact of the massive star formation on the surrounding interstellar medium in NGC1569 through a study of its stellar and dust properties. We use Herschel and ancillary multiwavelength observations, from the ultraviolet to the submillimeter regime, to construct its spectral energy distribution, which we model with magphys on ~300pc scales at the SPIRE250 μm resolution. The multiwavelength morphology shows low levels of dust emission in the cavity, and a concentration of several dust knots in its periphery. The extended emission seen in the ionised and neutral hydrogen observations is also present in the far-infrared emission. The dust mass is higher in the periphery of the cavity, driven by ongoing star formation and dust emission knots. The SFR is highest in the central region, while the specific SFR is more sensitive to the ongoing star formation. The region encompassing the cavity and SSCs contains only 12 per cent of the dust mass of the central starburst, in accord with other tracers of the interstellar medium. The gas-to-dust mass ratio is lower in the cavity and fluctuates to higher values in its periphery.

astro-ph.GA↗

arXiv2011

A New Catalog of HII Regions in M31

We present a new catalog of HII regions in M31. The full disk of the galaxy is covered in a 2.2 deg^2 mosaic of 10 fields observed with the Mosaic Camera as part of the Local Group Galaxies survey. We used HIIphot, a code for automated photometry of HII regions, to identify the regions and measure their fluxes and sizes. A 10 σ detection level was used to exclude diffuse gas fluctuations and star residuals after continuum subtraction. That selection limit may result in missing some faint HII regions, but our catalog of 3691 HII regions is still complete to a luminosity of LHα = 10^34 erg/s. This is five times fainter than the only previous CCD-based study which contained 967 objects in the NE half of M31. We determined the Hα luminosity function (LF) by fitting a power law to luminosities larger than LHα = 10^36.7 and determined a slope of 2.52\pm0.07. The in-arm and inter-arm LFs peak at different luminosities but they have similar bright-end slopes. The inter- arm regions are less populated (40% of total detected regions) and constitute only 14% of the total luminosity of LHα = 5.6 /times 10^40 erg/s (after extinction correction and considering 65% contribution from diffused ionized gas). A star formation rate of 0.44 M\odot/yr was estimated from the Hα total luminosity; this value is consistent with the determination from the Spitzer 8 μm image. We removed all known and potential planetary nebulae, yet we found a double peaked luminosity function. The inter-arm older population suggests a starburst between 15 and 20 million years ago. This result is in agreement with UV studies of the star formation history in M31 which found a star formation rate decrease in the recent past. We found a fair spatial correlation between the HII regions and stellar clusters in selected star forming regions. Most of the matched regions lie within the arm regions.

astro-ph.CO↗

arXiv2011

AEGIS: Demographics of X-ray and Optically Selected AGNs

We develop a new diagnostic method to classify galaxies into AGN hosts, star-forming galaxies, and absorption-dominated galaxies by combining the [O III]/Hbeta ratio with rest-frame U-B color. This can be used to robustly select AGNs in galaxy samples at intermediate redshifts (z<1). We compare the result of this optical AGN selection with X-ray selection using a sample of 3150 galaxies with 0.3 10^44 erg/s in our sample are not detected in our 200 ks Chandra images, most likely due to moderate or heavy absorption by gas near the AGN. The 2--7 keV detection rate of Seyfert 2s at z~0.6 suggests that their column density distribution and Compton-thick fraction are similar to that of local Seyferts. Multiple sample selection techniques are needed to obtain as complete a sample as possible.

astro-ph.CO↗

arXiv2010

The Submillimetre Universe

Submillimetre continuum radiation allows us to probe cold objects, particularly the earliest, dusty phases of star formation, high-redshift galaxies and circumstellar disks. The submillimetre window gives a unique view of the physical and dynamical conditions in the neutral and molecular interstellar medium. In the next decade a combination of wide-field surveys with single-dish telescopes and targeted follow-up with ALMA and other facilities should enable rapid progress in answering questions about the origins of planetary systems, stars and galaxies.

astro-ph.IM↗

arXiv2010

On the dust geometry in radio-loud active galactic nuclei

We use photometric and spectroscopic infrared observations obtained with the Spitzer Space Telescope of 12 radio-loud active galactic nuclei (AGN) to investigate the dust geometry. Our approach is to look at the change of the infrared spectral energy distribution (SED) and the strength of the 10 micron silicate feature with jet viewing angle. We find that (i) a combination of three or four blackbodies fits well the infrared SED; (ii) the sources viewed closer to the jet axis appear to have stronger warm (~300 - 800 K) and cold (~150 - 250 K) dust emissions relative to the hot component; and (iii) the silicate features are always in emission and strongly redshifted. We test clumpy torus models and find that (i) they approximate well the mid-infrared part of the SED, but significantly underpredict the fluxes at both near- and far-infrared wavelengths; (ii) they can constrain the dust composition (in our case to that of the standard interstellar medium); (iii) they require relatively large (~10%-20% the speed of light) redward displacements; and (iv) they give robust total mass estimates, but are insensitive to the assumed geometry.

astro-ph.CO↗

arXiv2009

The remnants of galaxy formation from a panoramic survey of the region around M31

In hierarchical cosmological models, galaxies grow in mass through the continual accretion of smaller ones. The tidal disruption of these systems is expected to result in loosely bound stars surrounding the galaxy, at distances that reach $10 - 100$ times the radius of the central disk. The number, luminosity and morphology of the relics of this process provide significant clues to galaxy formation history, but obtaining a comprehensive survey of these components is difficult because of their intrinsic faintness and vast extent. Here we report a panoramic survey of the Andromeda galaxy (M31). We detect stars and coherent structures that are almost certainly remnants of dwarf galaxies destroyed by the tidal field of M31. An improved census of their surviving counterparts implies that three-quarters of M31's satellites brighter than $M_V < -6$ await discovery. The brightest companion, Triangulum (M33), is surrounded by a stellar structure that provides persuasive evidence for a recent encounter with M31. This panorama of galaxy structure directly confirms the basic tenets of the hierarchical galaxy formation model and reveals the shared history of M31 and M33 in the unceasing build-up of galaxies.

astro-ph.CO↗

arXiv2008

Photometry using the Infrared Array Camera on the Spitzer Space Telescope

We present several corrections for point source photometry to be applied to data from the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. These corrections are necessary because of characteristics of the IRAC arrays and optics and the way the instrument is calibrated in-flight. When these corrections are applied, it is possible to achieve a ~2% relative photometric accuracy for sources of adequate signal to noise in an IRAC image.

astro-ph↗

arXiv2008

A point source survey of M31 with the Spitzer Space Telescope

We explore the stellar population of M31 in a Spitzer Space Telescope survey utilizing IRAC and MIPS observations. Red supergiants are the brightest objects seen in the infrared; they are a prominent evolutionary phase. Due to their circumstellar envelopes, many of these radiate the bulk of their luminosity at IRAC wavelengths and do not stand out in the near infrared or optically. Going fainter, we see large numbers of luminous asymptotic giant branch (AGB) stars, many of which are known long period variables. Relative to M33, the AGB carbon star population of M31 appears sparse, but this needs to be spectroscopically confirmed.

astro-ph↗

arXiv2008

Clusters of Galaxies in the First Half of the Universe from the IRAC Shallow Survey

We have identified 335 galaxy cluster and group candidates, 106 of which are at z > 1, using a 4.5 um selected sample of objects from a 7.25 deg^2 region in the Spitzer Infrared Array Camera (IRAC) Shallow Survey. Clusters were identified as 3-dimensional overdensities using a wavelet algorithm, based on photometric redshift probability distributions derived from IRAC and NOAO Deep Wide-Field Survey data. We estimate only ~10% of the detections are spurious. To date 12 of the z > 1 candidates have been confirmed spectroscopically, at redshifts from 1.06 to 1.41. Velocity dispersions of ~750 km/s for two of these argue for total cluster masses well above 10^14 M_sun, as does the mass estimated from the rest frame near infrared stellar luminosity. Although not selected to contain a red sequence, some evidence for red sequences is present in the spectroscopically confirmed clusters, and brighter galaxies are systematically redder than the mean galaxy color in clusters at all redshifts. The mean I - [3.6] color for cluster galaxies up to z ~ 1 is well matched by a passively evolving model in which stars are formed in a 0.1 Gyr burst starting at redshift z_f = 3. At z > 1, a wider range of formation histories is needed, but higher formation redshifts (i.e. z_f > 3) are favored for most clusters.

astro-ph↗