Publications by Aprajita Verma

Survey of Gravitationally-lensed Objects in HSC Imaging (SuGOHI): VI. Crowdsourced lens finding with Space Warps

Astronomy and Astrophysics 642 (2020)

A Sonnenfeld, A Verma, A More, E Baeten, C Macmillan, KC Wong, JHH Chan, AT Jaelani, CH Lee, M Oguri, CE Rusu, M Veldthuis, L Trouille, PJ Marshall, R Hutchings, C Allen, J O' Donnell, C Cornen, CP Davis, A McMaster, C Lintott, G Miller

© 2020 ESO. Context. Strong lenses are extremely useful probes of the distribution of matter on galaxy and cluster scales at cosmological distances, however, they are rare and difficult to find. The number of currently known lenses is on the order of 1000. Aims. The aim of this study is to use crowdsourcing to carry out a lens search targeting massive galaxies selected from over 442 square degrees of photometric data from the Hyper Suprime-Cam (HSC) survey. Methods. Based on the S16A internal data release of the HSC survey, we chose a sample of ∼300 000 galaxies with photometric redshifts in the range of 0.2 < zphot < 1.2 and photometrically inferred stellar masses of log M∗ > 11.2. We crowdsourced lens finding on this sample of galaxies on the Zooniverse platform as part of the Space Warps project. The sample was complemented by a large set of simulated lenses and visually selected non-lenses for training purposes. Nearly 6000 citizen volunteers participated in the experiment. In parallel, we used YATTALENS, an automated lens-finding algorithm, to look for lenses in the same sample of galaxies. Results. Based on a statistical analysis of classification data from the volunteers, we selected a sample of the most promising ∼1500 candidates, which we then visually inspected: half of them turned out to be possible (grade C) lenses or better. By including lenses found by YATTALENS or serendipitously noticed in the discussion section of the Space Warps website, we were able to find 14 definite lenses (grade A), 129 probable lenses (grade B), and 581 possible lenses. YATTALENS found half the number of lenses that were discovered via crowdsourcing. Conclusions. Crowdsourcing is able to produce samples of lens candidates with high completeness, when multiple images are clearly detected, and with higher purity compared to the currently available automated algorithms. A hybrid approach, in which the visual inspection of samples of lens candidates pre-selected by discovery algorithms or coupled to machine learning is crowdsourced, will be a viable option for lens finding in the 2020s, with forthcoming wide-area surveys such as LSST, Euclid, and WFIRST.

The rest-frame UV luminosity function at z≃4 : a significant contribution of AGN to the bright-end of the galaxy population

Monthly Notices of the Royal Astronomical Society Oxford University Press 494 (2020) 1771-1783

N Adams, R Bowler, M Jarvis, B Haussler, R McLure, A Bunker, J Dunlop, A Verma

We measure the rest-frame UV luminosity function (LF) at z ∼ 4 self-consistently over a wide range in absolute magnitude (−27 . MUV . −20). The LF is measured with 46,904 sources selected using a photometric redshift approach over ∼ 6 deg2 of the combined COSMOS and XMM-LSS fields. We simultaneously fit for both AGN and galaxy LFs using a combination of Schechter or Double Power Law (DPL) functions alongside a single power law for the faint-end slope of the AGN LF. We find a lack of evolution in the shape of the bright-end of the LBG component when compared to other studies at z ' 5 and evolutionary recipes for the UV LF. Regardless of whether the LBG LF is fit with a Schechter function or DPL, AGN are found to dominate at MUV < −23.5. We measure a steep faint-end slope of the AGN LF with αAGN = −2.09+0.35 −0.38 (−1.66+0.29 −0.58) when fit alongside a Schechter function (DPL) for the galaxies. Our results suggest that if AGN are morphologically selected it results in a bias to lower number densities. Only by considering the full galaxy population over the transition region from AGN to LBG domination can an accurate measurement of the total LF be attained.

Molecular gas inflows and outflows in ultraluminous infrared galaxies at z similar to 0.2 and one QSO at z=6.1

Astronomy and Astrophysics EDP Sciences 633 (2020) L4

R Herrera-Camus, E Sturm, J Gracia-Carpio, S Veilleux, T Shimizu, D Lutz, M Stone, E Gonzalez-Alfonso, R Davies, J Fischer, R Genzel, R Maiolino, A Sternberg, L Tacconi, A Verma

<p><strong>Aims:</strong> Our aim is to search for and characterize inflows and outflows of molecular gas in four ultraluminous infrared galaxies (ULIRGs; LIR >  1012L⊙) at z ∼ 0.2−0.3 and one distant quasi-stellar object (QSO) at z = 6.13.</p> <p><strong>Methods:</strong> We used Herschel/PACS and ALMA Band 7 observations of the hydroxyl molecule (OH) line at rest-frame wavelength 119 μm, which in absorption can provide unambiguous evidence of inflows or outflows of molecular gas in nuclear regions of galaxies. Our study contributes to doubling the number of OH 119 μm observations of luminous systems at z ∼ 0.2−0.3, and pushes the search for molecular outflows based on the OH 119 μm transition to z ∼ 6.</p> <p><strong>Results:</strong> We detect OH 119 μm high-velocity absorption wings in three of the four ULIRGs. In two cases, IRAS F20036−1547 and IRAS F13352+6402, the blueshifted absorption profiles indicate the presence of powerful and fast (∼200−500 km s−1) molecular gas outflows. Consistent with an inside-out quenching scenario, these outflows are depleting the central reservoir of star-forming molecular gas at a rate similar to that of intense star formation activity. For the starburst-dominated system IRAS 10091+4704, we detect an inverted P Cygni profile that is unique among ULIRGs and indicates the presence of a fast (∼400 km s−1) inflow of molecular gas at a rate of ∼100 M⊙ yr−1 towards the central region. Finally, we tentatively detect (∼3σ) the OH 119 μm doublet in absorption in the z = 6.13 QSO ULAS J131911+095051. The OH 119 μm feature is blueshifted with a median velocity that suggests the presence of a molecular outflow, although characterized by a modest molecular mass loss rate of ∼200 M⊙ yr−1. This value is comparable to the small mass outflow rates found in the stacking of the [C II] spectra of other z ∼ 6 QSOs and suggests that ejective feedback in this phase of the evolution of ULAS J131911+095051 has subsided.</p>

Better support for collaborations preparing for large-scale projects: the case study of the LSST Science Collaborations

Bulletin of the American Astronomical Society American Astronomical Society 51 (2019) 185
Part of a series from Astro2020 APC White Papers

FB Bianco, M Banerji, R Blum, J Bochanski, WN Brandt, P Burchat, J Gizis, Z Ivezić, C Keaton, S Kaviraj, T Loredo, R Mandelbaum, P Marshall, P McGehee, C Schafer, ME Schwamb, JL Sokoloski, MA Strauss, R Street, D Trilling, A Verma

Through the lens of the LSST Science Collaborations’ experience, we advocate for new, improved ways to fund large, complex collaborations as they work in preparation for and on peta-scale surveys. We advocate for the establishment of programs to support research and infrastructure that enables innovative collaborative research on such scales.

What do astronomers want from the STFC?

Astronomy and Geophysics Oxford University Press 60 (2019) 2.13-2.17

S Serjeant, J Bolton, P Gandhi, C Helling, P Mazzali, B Stappers, Y Unruh, A Verma

Stephen Serjeant and the STFC's Astronomy Advisory Panel summarize community responses to its consultation on research priorities, undertaken in November 2018.

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

Monthly Notices of the Royal Astronomical Society Oxford University Press 481 (2018) 3497-3519

A Saintonge, CD Wilson, T Xiao, L Lin, HS Hwang, T Tosaki, M Bureau, PJ Cigan, CJR Clark, DL Clements, ID Looze, T Dharmawardena, Y Gao, WK Gear, J Greenslade, I Lamperti, JC Lee, C Li, MJ Michałowski, A Mok, HA Pan, AE Sansom, M Sargent, MW Matthew, T Williams

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 850 µm continuum measurements with SCUBA-2 for a representative sample of 193 Herschel-selected galaxies with M* &gt; 109 M⊙, 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 multiwavelength 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 catalogue with derived properties, and introduce the JINGLE Main Data Release. Science highlights include the non-linearity of the relation between 850 µm luminosity and CO line luminosity (log LCO(2–1) =  1.372 logL850–1.376), and the serendipitous discovery of candidate z &gt; 6 galaxies.

Resolving star formation on subkiloparsec scales in the high-redshift galaxy SDP.11 using gravitational lensing

Astrophysical Journal American Astronomical Society 867 (2018) 140

C Lamarche, A Verma, A Vishwas, GJ Stacey, D Brisbin, C Ferkinhoff, T Nikola, SJU Higdon, J Higdon, M Tecza

We investigate the properties of the interstellar medium, star formation, and the current-day stellar population in the strongly lensed star-forming galaxy H-ATLAS J091043.1-000321 (SDP.11), at z = 1.7830, using new Herschel and Atacama Large Millimeter/submillimeter Array (ALMA) observations of far-infrared fine-structure lines of carbon, oxygen, and nitrogen. We report detections of the [O iii] 52 μm, [N iii] 57 μm, and [O i] 63 μm lines from Herschel/PACS, and present high-resolution imaging of the [C ii] 158 μm line, and underlying continuum, using ALMA. We resolve the [C ii] line emission into two spatially offset Einstein rings, tracing the red and blue velocity components of the line, in the ALMA/Band 9 observations at 0farcs2 resolution. The values seen in the [C ii]/far-infrared (FIR) ratio map, as low as ~0.02% at the peak of the dust continuum, are similar to those of local ULIRGs, suggesting an intense starburst in this source. This is consistent with the high intrinsic FIR luminosity (~3 × 1012 L ⊙), ~16 Myr gas depletion timescale, and lesssim8 Myr timescale since the last starburst episode, estimated from the hardness of the UV radiation field. By applying gravitational lensing models to the visibilities in the uv-plane, we find that the lensing magnification factor varies by a factor of two across SDP.11, affecting the observed line profiles. After correcting for the effects of differential lensing, a symmetric line profile is recovered, suggesting that the starburst present here may not be the result of a major merger, as is the case for local ULIRGs, but instead could be powered by star formation activity spread across a 3–5 kpc rotating disk.

Strong lensing considerations for the LSST observing strategy


A Verma, T Collett, GP Smith

Strong gravitational lensing enables a wide range of science: probing cosmography; testing dark matter models; understanding galaxy evolution; and magnifying the faint, small and distant Universe. However to date exploiting strong lensing as a tool for these numerous cosmological and astrophysical applications has been severely hampered by limited sample sized. LSST will drive studies of strongly lensed galaxies, galaxy groups and galaxy clusters into the statistical age. Time variable lensing events, e.g. measuring cosmological time delays from strongly lensed supernovae and quasars, place the strongest constraints on LSST's observing strategy and have been considered in the DESC observing strategy white papers. Here we focus on aspects of `static' lens discovery that will be affected by the observing strategy. In summary, we advocate (1) ensuring comparable (sub-arcsecond) seeing in the g-band as in r and i to facilitate discovery of gravitational lenses, and (2) initially surveying the entire observable extragalactic sky as rapidly as possible to enable early science spanning a broad range of static and transient interests.

SHINING, A Survey of Far-infrared Lines in Nearby Galaxies. I. Survey Description, Observational Trends, and Line Diagnostics


R Herrera-Camus, E Sturm, J Gracia-Carpio, D Lutz, A Contursi, S Veilleux, J Fischer, E Gonzalez-Alfonso, A Poglitsch, L Tacconi, R Genzel, R Maiolino, A Sternberg, R Davies, A Verma

SHINING, A Survey of Far-infrared Lines in Nearby Galaxies. II. Line-deficit Models, AGN Impact, [C II]-SFR Scaling Relations, and Mass-Metallicity Relation in (U)LIRGs


R Herrera-Camus, E Sturm, J Gracia-Carpio, D Lutz, A Contursi, S Veilleux, J Fischer, E Gonzalez-Alfonso, A Poglitsch, L Tacconi, R Genzel, R Maiolino, A Sternberg, R Davies, A Verma

Models of gravitational lens candidates from Space Warps CFHTLS


R Kung, P Saha, I Ferreras, E Baeten, J Coles, C Cornen, C Macmillan, P Marshall, A More, L Oswald, A Verma, JK Wilcox

Lensing galaxies in the CFHT Legacy Survey

14th Marcel Grossman Meeting On Recent Developments in Theoretical and Experimental General Relativity, Astrophysics and Relativistic Field Theories, Proceedings (2018) 2997-3002

R Küng, P Saha, J Coles, I Ferreras, P Marshall, A More, S More, A Verma, E Baeten, C Cornen, C Macmillan, JK Wilcox

Copyright © 2018 by the Editors.All rights reserved. In Space Warps, a community of over 30 000 volunteers searched for lensed candidates in the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). 59 new lens candidates have been identified, along with rediscovery of 60% of the previously-known candidates.1 We propose that volunteers should play an integral part in the modeling of lens candidates as well. We implemented SpaghettiLens, a method allowing non-professionals to create mass models for those discovered lens candidates and to be usable in a citizen-science environment. Tests with simulated lenses show that models by experienced volunteers are comparable to those by experts.2 We present models of most of the Space Warps lens candidates that were produced collaboratively by a small community of lens enthusiasts from the volunteer community. These models allow for further analysis.

Interstellar medium conditions in z similar to 0.2 Lyman-break analogs


A Contursi, AJ Baker, S Berta, B Magnelli, D Lutz, J Fischer, A Verma, M Nielbock, JG Carpio, S Veilleux, E Sturm, R Davies, R Genzel, S Hailey-Dunsheath, R Herrera-Camus, A Janssen, A Poglitsch, A Sternberg, LJ Tacconi

Evidence that the AGN dominates the radio emission in z ~ 1 radio-quiet quasars

Monthly Notices of the Royal Astronomical Society Oxford University Press 468 (2017) 217-238

SV White, M Jarvis, E Kalfountzou, MJ Hardcastle, A Verma, JM Cao Orjales, J Stevens

<p>In order to understand the role of radio-quiet quasars (RQQs) in galaxy evolution, we must determine the relative levels of accretion and star-formation activity within these objects. Previous work at low radio flux densities has shown that accretion makes a significant contribution to the total radio emission, in contrast with other quasar studies that suggest star formation dominates. To investigate, we use 70 RQQs from the <em>Spitzer-Herschel</em> Active Galaxy Survey. These quasars are all at <em>z</em> &amp;Tilde; 1, thereby minimizing evolutionary effects, and have been selected to span a factor of &amp;Tilde;100 in optical luminosity, so that the luminosity dependence of their properties can be studied. We have imaged the sample using the Karl G. Jansky Very Large Array (JVLA), whose high sensitivity results in 35 RQQs being detected above 2σ. This radio data set is combined with far-infrared luminosities derived from grey-body fitting to <em>Herschel</em> photometry. By exploiting the far-infrared-radio correlation observed for star-forming galaxies, and comparing two independent estimates of the star-formation rate, we show that star formation alone is not sufficient to explain the total radio emission. Considering RQQs above a 2σ detection level in both the radio and the far-infrared, 92 per cent are accretion dominated, and the accretion process accounts for 80 per cent of the radio luminosity when summed across the objects. The radio emission connected with accretion appears to be correlated with the optical luminosity of the RQQ, whilst a weaker luminosity dependence is evident for the radio emission connected with star formation.</p>

The interstellar medium in high-redshift submillimeter galaxies as probed by infrared spectroscopy

Astrophysical Journal IOP Publishing 837 (2017)

JL Wardlow, A Cooray, W Osage, N Bourne, D Clements, H Dannerbauer, L Dunne, S Dye, S Eales, D Farrah, C Furlanetto, E Ibar, R Ivison, S Maddox, MM Michałowski, D Riechers, D Rigopoulou, D Scott, MWL Smith, L Wang, PVD Werf, E Valiante, I Valtchanov, A Verma

Submillimeter galaxies (SMGs) at $z\gtrsim1$ are luminous in the far-infrared and have star-formation rates, SFR, of hundreds to thousands of solar masses per year. However, it is unclear whether they are true analogs of local ULIRGs or whether the mode of their star formation is more similar to that in local disk galaxies. We target these questions by using Herschel-PACS to examine the conditions in the interstellar medium (ISM) in far-infrared luminous SMGs at z~1-4. We present 70-160 micron photometry and spectroscopy of the [OIV]26 micron, [FeII]26 micron, [SIII]33 micron, [SiII]34 micron, [OIII]52 micron, [NIII]57 micron, and [OI]63 micron fine-structure lines and the S(0) and S(1) hydrogen rotational lines in 13 lensed SMGs identified by their brightness in early Herschel data. Most of the 13 targets are not individually spectroscopically detected and we instead focus on stacking these spectra with observations of an additional 32 SMGs from the \herschel\ archive -- representing a complete compilation of PACS spectroscopy of SMGs. We detect [OI]63 micron, [SiII]34 micron, and [NIII]57 micron at &gt;3sigma in the stacked spectra, determining that the average strengths of these lines relative to the far-IR continuum are $(0.36\pm0.12)\times10^{-3}$, $(0.84\pm0.17)\times10^{-3}$, and $(0.27\pm0.10)\times10^{-3}$, respectively. Using the [OIII]52/[NIII]57 emission line ratio we show that SMGs have average gas-phase metallicities $\gtrsim Z_{\rm sun}$. By using PDR modelling and combining the new spectral measurements with integrated far-infrared fluxes and existing [CII]158 micron data we show that SMGs have average gas densities, n, of $\sim10^{1-3}{\rm cm^{-3}}$ and FUV field strengths, $G_0\sim10^{2.2-4.5}$ (in Habing units: $1.6\times10^{-3}{\rm erg~cm^{-2}~s^{-1}}$), consistent with both local ULIRGs and lower luminosity star-forming galaxies.

The WEAVE-LOFAR survey

Proceedings SF2A 2016 - Scientific highlights Société Francaise d’Astronomie et d’Astrophysique (SF2A) (2016) 271-280

DJB Smith, PN Best, KJ Duncan, NA Hatch, MJ Jarvis, HJA Röttgering, CJ Simpson, JP Stott, RK Cochrane, KE Coppin, H Dannerbauer, TA Davis, JE Geach, CL Hale, MJ Hardcastle, PW Hatfield, RCW Houghton, N Maddox, SL McGee, L Morabito, D Nisbet, M Pandey-Pommier, I Prandoni, A Saxena, TW Shimwell

In these proceedings we highlight the primary scientific goals and design of the WEAVE-LOFAR survey, which will use the new WEAVE spectrograph on the 4.2m William Herschel Telescope to provide the primary source of spectroscopic information for the LOFAR Surveys Key Science Project. Beginning in 2018, WEAVE-LOFAR will generate more than 10$^6$ R=5000 365-960 nm spectra of low-frequency selected radio sources, across three tiers designed to efficiently sample the redshift-luminosity plane, and produce a data set of enormous legacy value. The radio frequency selection, combined with the high multiplex and throughput of the WEAVE spectrograph, make obtaining redshifts in this way very efficient, and we expect that the redshift success rate will approach 100 per cent at $z &lt; 1$. This unprecedented spectroscopic sample - which will be complemented by an integral field component - will be transformational in key areas, including studying the star formation history of the Universe, the role of accretion and AGN-driven feedback, properties of the epoch of reionisation, cosmology, cluster haloes and relics, as well as the nature of radio galaxies and protoclusters. Each topic will be addressed in unprecedented detail, and with the most reliable source classifications and redshift information in existence.



JE Geach, D Narayanan, Y Matsuda, M Hayes, L Mas-Ribas, M Dijkstra, CC Steidel, SC Chapman, R Feldmann, A Avison, O Agertz, Y Ao, M Birkinshaw, MN Bremer, DL Clements, H Dannerbauer, D Farrah, CM Harrison, M Kubo, MJ Michalowski, D Scott, DJB Smith, M Spaans, JM Simpson, AM Swinbank, Y Taniguchi, P van der Werf, A Verma, T Yamada

The galaxy–halo connection in the VIDEO survey at 0.5 &lt; z &lt; 1.7

Monthly Notices of the Royal Astronomical Society Oxford University Press 459 (2016) 2618-2631

PETER Hatfield, Lindsay, M Jarvis, B Häußler, M Vaccari, A Verma

We present a series of results from a clustering analysis of the first data release of the Visible and Infrared Survey Telescope for Astronomy (VISTA) Deep Extragalactic Observations (VIDEO) survey. VIDEO is the only survey currently capable of probing the bulk of stellar mass in galaxies at redshifts corresponding to the peak of star formation on degree scales. Galaxy clustering is measured with the two-point correlation function, which is calculated using a non-parametric kernel-based density estimator. We use our measurements to investigate the connection between the galaxies and the host dark matter halo using a halo occupation distribution methodology, deriving bias, satellite fractions, and typical host halo masses for stellar masses between 10 9.35 and 10 10.85 M ⊙ , at redshifts 0.5 &lt; z &lt; 1.7. Our results show typical halo mass increasing with stellar mass (with moderate scatter) and bias increasing with stellar mass and redshift consistent with previous studies. We find that the satellite fraction increased towards low redshifts, from ~5 per cent at z ~ 1.5 to ~20 per cent at z ~ 0.6. We combine our results to derive the stellar mass-to-halo mass ratio for both satellites and centrals over a range of halo masses and find the peak corresponding to the halo mass with maximum star formation efficiency to be ~2 × 10 12 M ⊙ , finding no evidence for evolution.



AW Janssen, N Christopher, E Sturm, S Veilleux, A Contursi, E Gonzalez-Alfonso, J Fischer, R Davies, A Verma, J Gracia-Carpio, R Genzel, D Lutz, A Sternberg, L Tacconi, L Burtscher, A Poglitsch

Space Warps II. New gravitational lens candidates from the CFHTLS discovered through citizen science

Monthly Notices of the Royal Astronomical Society Oxford University Press 455 (2015) 1191-1210

A More, A Verma, PJ Marshall, S More, E Baeten, J Wilcox, C Macmillan, C Cornen, A Kapadia, M Parrish, C Snyder, CP Davis, R Gavazzi, CJ Lintott, R Simpson, D Miller, AM Smith, E Paget, P Saha, R Küng, TE Collett

We report the discovery of 29 promising (and 59 total) new lens candidates from the CFHT Legacy Survey (CFHTLS) based on about 11 million classifications performed by citizen scientists as part of the first Space Warps lens search. The goal of the blind lens search was to identify lens candidates missed by robots (the RingFinder on galaxy scales and ArcFinder on group/cluster scales) which had been previously used to mine the CFHTLS for lenses. We compare some properties of the samples detected by these algorithms to the Space Warps sample and find them to be broadly similar. The image separation distribution calculated from the Space Warps sample shows that previous constraints on the average density profile of lens galaxies are robust. SpaceWarps recovers about 65% of known lenses, while the new candidates show a richer variety compared to those found by the two robots. This detection rate could be increased to 80% by only using classifications performed by expert volunteers (albeit at the cost of a lower purity), indicating that the training and performance calibration of the citizen scientists is very important for the success of Space Warps. In this work we present the SIMCT pipeline, used for generating in situ a sample of realistic simulated lensed images. This training sample, along with the false positives identified during the search, has a legacy value for testing future lens finding algorithms. We make the pipeline and the training set publicly available.