# Dr Noelia E. D. Noël

Lecturer in Astrophysics
PhD in Astrophysics, FHEA
+44 (0)1483 683590
20 BC 03

Astrophysics Research Group.

## Publications

W. Cerny, Joshua D. Simon, TIANRU LI, A Drlica-Wagner, A.B Pace, C. E Martınez-Vazquez, A. H. Riley, B. Mutlu-Pakdil, S Mau, P. S. Ferguson, DENIS ERKAL, Ricardo R. Muñoz, C. R Bom, J. L. Carlin, D. Carollo, Y. Choi, A. P. Ji, D Martınez-Delgado, V Manwadkar, A. E Miller, NOELIA ESTELLA DONATA NOEL, Joanna D Sakowska, D. J. Sand, G. S. Stringfellow, E. J. Tollerud, AK Vivas, Julio A. Carballo-Bello, D. Hernandez-Lang, DEBORAH JAMES, J. L. Nilo Castellon, K. A. G Olsen, A. Zenteno (2022)Pegasus IV: Discovery and Spectroscopic Confirmation of an Ultra-Faint Dwarf Galaxy in the Constellation Pegasus

We report the discovery of Pegasus IV, an ultra-faint dwarf galaxy found in archival data from the Dark Energy Camera processed by the DECam Local Volume Exploration Survey. Pegasus IV is a compact, ultra-faint stellar system ($r_{1/2} = 41^{+8}_{-6}$ pc; $M_V = -4.25 \pm 0.2$ mag) located at a heliocentric distance of $90^{+4}_{-6}$ kpc. Based on spectra of seven non-variable member stars observed with Magellan/IMACS, we confidently resolve Pegasus IV's velocity dispersion, measuring $\sigma_{v} = 3.3^{+1.7}_{-1.1} \text{ km s}^{-1}$ (after excluding three velocity outliers); this implies a mass-to-light ratio of $M_{1/2}/L_{V,1/2} = 167^{+224}_{-99} M_{\odot}/L_{\odot}$ for the system. From the five stars with the highest signal-to-noise spectra, we also measure a systemic metallicity of $\rm [Fe/H] = -2.67^{+0.25}_{-0.29}$ dex, making Pegasus IV one of the most metal-poor ultra-faint dwarfs. We tentatively resolve a non-zero metallicity dispersion for the system. These measurements provide strong evidence that Pegasus IV is a dark-matter-dominated dwarf galaxy, rather than a star cluster. We measure Pegasus IV's proper motion using data from Gaia Early Data Release 3, finding ($\mu_{\alpha*}, \mu_{\delta}) = (0.33\pm 0.07, -0.21 \pm 0.08) \text{ mas yr}^{-1}$. When combined with our measured systemic velocity, this proper motion suggests that Pegasus IV is on an elliptical, retrograde orbit, and is currently near its orbital apocenter. Lastly, we identify three potential RR Lyrae variable stars within Pegasus IV, including one candidate member located more than ten half-light radii away from the system's centroid. The discovery of yet another ultra-faint dwarf galaxy strongly suggests that the census of Milky Way satellites is still incomplete, even within 100 kpc.

A Drlica-Wagner, P. S. Ferguson, M. Adamów, M Aguena, F Andrade-Oliveira, D Bacon, K Bechtol, Eric F. Bell, E Bertin, P Bilaji, S Bocquet, C. R Bom, D Brooks, DL Burke, Julio A. Carballo-Bello, J. L. Carlin, AC Rosell, MC Kind, J Carretero, FJ Castander, W. Cerny, Chao-Hsi Chang, Y. Choi, C Conselice, M Costanzi, D. Crnojević, LN da Costa, J. De Vicente, S Desai, J Esteves, S. Everett, I Ferrero, MF Fitzpatrick, B Flaugher, D Friedel, J Frieman, J. Garcia-Bellido, M Gatti, E Gaztanaga, DW Gerdes, D Gruen, RA Gruendl, J. Gschwend, W Hartley, D. Hernandez-Lang, S. R Hinton, D.L Hollowood, K Honscheid, ASHLEY KATE HUGHES, A Jacques, DEBORAH JAMES, M. D Johnson, K Kuehn, N Kuropatkin, O Lahav, TIANRU LI, C. Lidman, Hong Lin, M March, J. L. Marshall, D Martinez-Delgado, C. E. Martínez-Vázquez, POL MASSANA ZAPATA, S Mau, M. McNanna, P Melchior, F. Menanteau, A. E Miller, R Miquel, J Mohr, R Morgan, B. Mutlu-Pakdil, Ricardo R. Muñoz, E Neilsen, David L Nidever, R Nikutta, J. L. Nilo Castellon, NOELIA ESTELLA DONATA NOEL, R L C Ogando, K. A. G Olsen, A.B Pace, A. Palmese, F. Paz-Chinchon, M. E. S Pereira, A Pieres, A. A. Plazas Malagón, J Prat, A. H. Riley, M Rodriguez-Monroy, AK Romer, A Roodman, M Sako, Joanna D Sakowska, E Sanchez, F. J Sánchez, D. J. Sand, L. Santana-Silva, B Santiago, M Schubnell, S. Serrano, I Sevilla-Noarbe, Joshua D. Simon, MATTHEW LLOYD SMITH, M Soares-Santos, G Stringfellow, E Suchyta, DJ Suson, C. Y Tan, G Tarle, K. Tavangar, DR Thomas, Cheryl To, E. J. Tollerud, M. A Troxel, D Tucker, T. N Varga, AK Vivas, Alistair Walker, JODIE WELLER, Ryan Wilkinson, J. Wu, B Yanny, E Zaborowski, A. Zenteno (2022)The DECam Local Volume Exploration Survey Data Release 2, In: The Astrophysical journal Supplement series261(2) IOP Publishing

We present the second public data release (DR2) from the DECam Local Volume Exploration survey (DELVE). DELVE DR2 combines new DECam observations with archival DECam data from the Dark Energy Survey, the DECam Legacy Survey, and other DECam community programs. DELVE DR2 consists of ~160,000 exposures that cover >21,000 deg^2 of the high Galactic latitude (|b| > 10 deg) sky in four broadband optical/near-infrared filters (g, r, i, z). DELVE DR2 provides point-source and automatic aperture photometry for ~2.5 billion astronomical sources with a median 5{\sigma} point-source depth of g=24.3, r=23.9, i=23.5, and z=22.8 mag. A region of ~17,000 deg^2 has been imaged in all four filters, providing four-band photometric measurements for ~618 million astronomical sources. DELVE DR2 covers more than four times the area of the previous DELVE data release and contains roughly five times as many astronomical objects. DELVE DR2 is publicly available via the NOIRLab Astro Data Lab science platform.

Pol Massana, T. Ruiz-Lara, Noelia E. D. Noël, C Gallart, David L Nidever, Y. Choi, Joanna D Sakowska, Gurtina Besla, K. A. G Olsen, Mateo Monelli, A Dorta, G. S. Stringfellow, S. Cassisi, Edouard Bernard, Dennis Zaritsky, Maria-Rosa L. Cioni, Antonela Monachesi, Roeland van der Marel, T. J. L de Boer, Alistair Walker (2022)The synchronised dance of the Magellanic Clouds' star formation history, In: Monthly Notices of the Royal Astronomical Society: Letters513(1)pp. L40-L45

We use the SMASH survey to obtain unprecedented deep photometry reaching down to the oldest main sequence turn-offs in the colour-magnitude diagrams (CMDs) of the Small Magellanic Cloud (SMC) and quantitatively derive its star formation history (SFH) using CMD fitting techniques. We identify five distinctive peaks of star formation in the last 3.5 Gyr, at $\sim$3, $\sim$2, $\sim$1.1, $\sim$0.45 Gyr ago, and one presently. We compare these to the SFH of the Large Magellanic Cloud (LMC) finding unequivocal synchronicity, with both galaxies displaying similar periods of enhanced star formation over the past $\sim$3.5 Gyr. The parallelism between their SFHs indicates that tidal interactions between the MCs have recurrently played an important role in their evolution for at least the last $\sim$3.5 Gyr, tidally truncating the SMC and shaping the LMC's spiral arm. We show, for the first time, an SMC-LMC correlated SFH at recent times in which enhancements of star formation are localised in the northern spiral arm of the LMC, and globally across the SMC. These novel findings should be used to constrain not only the orbital history of the MCs but also how star formation should be treated in simulations.

S. Mau, W. Cerny, A.B Pace, Y. Choi, A. Drlica-Wagner, L. Santana-Silver, A.H Riley, Denis Erkal, S. Stringfellow, M. Adamow, J.L Carlin, R.A Gruendal, D. Hernandez-Lang, N. Kuropatkin, T.S Li, C.E Martinez-Vasquez, E. Morganson, B. Mutlu-Pakdil, E.H Neilsen, D.L Nidever, K.A.G Olsen, D.J Sand, E.J Tollerud, D.L Tucker, B. Yanny, A. Zenteno, S. Allam, W.A Barkhouse, K. Bechtol, E.F Bell, P. Balaji, D. Crnojevic, J. Esteves, P.S Ferguson, C. Gallart, A.K Hughes, D.J James, P. Jethwa, L.C Johnson, K. Kuehn, S. Majewski, Y-Y. Mao, P. Massana, M. McNanna, A. Monachesi, E.O Nadler, Noelia Noel, A. Palmese, F. Paz-Chinchon, A. Pieres, J. Sanchez, N. Shipp, J.D Simon, M. Soares-Santos, K. Tavangar, R.P van der Marel, A.K Vivas, A.R Walker, R.H Wechsler (2020)Two Ultra-Faint Milky Way Stellar Systems Discovered in Early Data from the DECam Local Volume Exploration Survey, In: Astrophysical Journal American Astronomical Society

We report the discovery of two ultra-faint stellar systems found in early data from the DECam Local Volume Exploration survey (DELVE). The rst system, Centaurus I (DELVE J1238

G Torrealba, V Belokurov, S Koposov, K Bechtol, A Drlica-Wagner, K Olsen, A Vivas, B Yanny, P Jethwa, A Walker, T Li, S Allam, B Conn, C Gallart, R Gruendl, D James, M Johnson, K Kuehn, N Kuropatkin, N Martin, D Martinez-Delgado, D Nidever, Noelia Noel, J Simon, G Stringfellow, D Tucker (2018)Discovery of two neighbouring satellites in the Carina constellation with MagLiteS, In: Monthly Notices of the Royal Astronomical Society475(4)pp. 5085-5097 Oxford University Press

We report the discovery of two ultra-faint satellites in the vicinity of the Large Magellanic Cloud (LMC) in data from the Magellanic Satellites Survey (MagLiteS ). Situated 18 deg (∼20 kpc) from the LMC and separated from each other by only 18 arcmin, Carina II and III form an intriguing pair. By simultaneously modelling the spatial and the colour–magnitude stellar distributions, we find that both Carina II and Carina III are likely dwarf galaxies, although this is less clear for Carina III. There are in fact several obvious differences between the two satellites. While both are well described by an old and metal poor population, Carina II is located at ∼36 kpc from the Sun, with MV ∼ −4.5 and rh ∼ 90 pc, and it is further confirmed by the discovery of 3 RR Lyrae at the right distance. In contrast, Carina III is much more elongated, measured to be fainter (MV ∼ −2.4), significantly more compact (rh ∼ 30 pc), and closer to the Sun, at ∼28 kpc, placing it only 8 kpc away from Car II. Together with several other systems detected by the Dark Energy Camera, Carina II and III form a strongly anisotropic cloud of satellites in the vicinity of the Magellanic Clouds.

Yumi Choi, David L. Nidever, Knut Olsen, Gurtina Besla, Robert D. Blum, Dennis Zaritsky, Maria-Rosa L. Cioni, Roeland P. van der Marel, Eric F. Bell, L. Clifton Johnson, A. Katherina Vivas, Alistair R. Walker, Thomas J. L. de Boer, Noelia E. D. Noel, Antonela Monachesi, Carme Gallart, Matteo Monelli, Guy S. Stringfellow, Pol Massana, David Martinez-Delgado, Ricardo R. Muñoz (2018)SMASHing the LMC: Mapping a Ring-like Stellar Overdensity in the LMC Disk, In: The Astrophysical Journal869(2)125 IOP Publishing

We explore the stellar structure of the Large Magellanic Cloud (LMC) disk using data from the Survey of the MAgellanic Stellar History and the Dark Energy Survey. We detect a ring-like stellar overdensity in the red clump star count map at a radius of ~6° (~5.2 kpc at the LMC distance) that is continuous over ~270° in position angle and is only limited by the current data coverage. The overdensity shows an amplitude up to 2.5 times higher than that of the underlying smooth disk. This structure might be related to the multiple arms found by de Vaucouleurs. We find that the overdensity shows spatial correlation with intermediate-age star clusters, but not with young (

David Martínez-Delgado, Anna Katherina Vivas, Eva K. Grebel, Carme Gallart, Adriano Pieres, Cameron P. M. Bell, Paul Zivick, Bertrand Lemasle, Lent Clifton Johnson, Julio A. Carballo-Bello, Noelia E.D Noel, Maria-Rosa L. Cioni, Yumi Choi, Gurtina Besla, Judy Schmidt, Dennis Zaritsky, Robert A. Gruendl, Mark Seibert, David Nidever, Laura Monteagudo, Mateo Monelli, Bernhard Hubl, Roeland van der Marel, Fernando J. Ballesteros, Guy Stringfellow, Alistair Walker, Robert Blum, Eric F. Bell, Blair C. Conn, Knut Olsen, Nicolas Martin, You-Hua Chu, Laura Inno, Thomas J. L. Boer, Nitya Kallivayalil, Michele De Leo, Yuri Beletsky, Fabian Neyer, Ricardo R. Muñoz (2019)Nature of a shell of young stars in the outskirts of the Small Magellanic Cloud, In: Astronomy & Astrophysics631A98 EDP Sciences

Context. Understanding the evolutionary history of the Magellanic Clouds requires an in-depth exploration and characterization of the stellar content in their outer regions, which ultimately are key to tracing the epochs and nature of past interactions. Aims. We present new deep images of a shell-like overdensity of stars in the outskirts of the Small Magellanic Cloud (SMC). The shell, also detected in photographic plates dating back to the fifties, is located at ∼1.9° from the center of the SMC in the north-east direction. Methods. The structure and stellar content of this feature were studied with multiband, optical data from the Survey of the MAgellanic Stellar History (SMASH) carried out with the Dark Energy Camera on the Blanco Telescope at Cerro Tololo Inter-American Observatory. We also investigate the kinematic of the stars in the shell using the Gaia Data Release 2. Results. The shell is composed of a young population with an age ∼150 Myr, with no contribution from an old population. Thus, it is hard to explain its origin as the remnant of a tidally disrupted stellar system. The spatial distribution of the young main-sequence stars shows a rich sub-structure, with a spiral arm-like feature emanating from the main shell and a separated small arc of young stars close to the globular cluster NGC 362. We find that the absolute g-band magnitude of the shell is Mg, shell = −10.78 ± 0.02, with a surface brightness of μg, shell = 25.81 ± 0.01 mag arcsec−2. Conclusion. We have not found any evidence that this feature is of tidal origin or a bright part of a spiral arm-like structure. Instead, we suggest that the shell formed in a recent star formation event, likely triggered by an interaction with the Large Magellanic Cloud and or the Milky Way, ∼150 Myr ago.

T. S. Li, J. D. Simon, A. B. Pace, G. Torrealba, K. Kuehn, A. Drlica-Wagner, K. Bechtol, A. K. Vivas, R. P. van der Marel, M. Wood, B. Yanny, V. Belokurov, P. Jethwa, D. B. Zucker, G. Lewis, R. Kron, D. L. Nidever, M. A. Sánchez-Conde, A. P. Ji, B. C. Conn, D. J. James, N. F. Martin, D. Martinez-Delgado, N. E. D. Noel (2018)Ships Passing in the Night: Spectroscopic Analysis of Two Ultra-faint Satellites in the Constellation Carina, In: The Astrophysical Journal857(2)145 IOP Publishing

We report the discovery of two ultra-faint satellites in the vicinity of the Large Magellanic Cloud (LMC) in data from the Magellanic Satellites Survey (MagLiteS ). Situated 18 deg (∼20 kpc) from the LMC and separated from each other by only 18 arcmin, Carina II and III form an intriguing pair. By simultaneously modelling the spatial and the colour–magnitude stellar distributions, we find that both Carina II and Carina III are likely dwarf galaxies, although this is less clear for Carina III. There are in fact several obvious differences between the two satellites. While both are well described by an old and metal poor population, Carina II is located at ∼36 kpc from the Sun, with MV ∼ −4.5 and rh ∼ 90 pc, and it is further confirmed by the discovery of 3 RR Lyrae at the right distance. In contrast, Carina III is much more elongated, measured to be fainter (MV ∼ −2.4), significantly more compact (rh ∼ 30 pc), and closer to the Sun, at ∼28 kpc, placing it only 8 kpc away from Car II. Together with several other systems detected by the Dark Energy Camera, Carina II and III form a strongly anisotropic cloud of satellites in the vicinity of the Magellanic Clouds.

Cameron P. M. Bell, Maria-Rosa L. Cioni, A H Wright, Stefano Rubele, David L Nidever, Ben L Tatton, Jacco Th van Loon, Dennis Zaritsky, Yumi Choi, Samyaday Samyaday, Gisella Clementini, Richard de Grijs, Valentin D Ivanov, Steven R Majewski, Marcella Marconi, David Martínez-Delgado, POL MASSANA ZAPATA, Ricardo R. Muñoz, Florian Niederhofer, NOELIA ESTELLA DONATA NOEL, Joana M Oliveira, Knut Olsen, Clara M Pennock, V Ripepi, Smitha Subramanian, A Katherina Vivas (2020)The intrinsic reddening of the Magellanic Clouds as traced by background galaxies – II. The Small Magellanic Cloud, In: Monthly Notices of the Royal Astronomical Society499(1)pp. 993-1004 OUP

We present a map of the total intrinsic reddening across ≃34 deg2 of the Small Magellanic Cloud (SMC) derived using optical (ugriz) and near-infrared (IR; YJKs) spectral energy distributions (SEDs) of background galaxies. The reddening map is created using a subsample of 29 274 galaxies with low levels of intrinsic reddening based on the LEPHARE χ2 minimization SED-fitting routine. We find statistically significant enhanced levels of reddening associated with the main body of the SMC compared with regions in the outskirts [ΔE(B − V) ≃ 0.3 mag]. A comparison with literature reddening maps of the SMC shows that, after correcting for differences in the volume of the SMC sampled, there is good agreement between our results and maps created using young stars. In contrast, we find significant discrepancies between our results and maps created using old stars or based on longer wavelength far-IR dust emission that could stem from biased samples in the former and uncertainties in the far-IR emissivity and the optical properties of the dust grains in the latter. This study represents one of the first large-scale categorizations of extragalactic sources behind the SMC and as such we provide the LEPHARE outputs for our full sample of ∼500 000 sources.

David L Nidever, Knut Olsen, Yumi Choi, Tomas Ruiz-Lara, Amy E Miller, L. Clifton Johnson, Cameron P. M Bell, Robert D Blum, Maria-Rosa L Cioni, Carme Gallart, Steven R Majewski, Nicolas F Martin, Pol Massana, Antonela Monachesi, Noelia E. D Noel, Joanna D Sakowska, Roeland P van der Marel, Alistair R Walker, Dennis Zaritsky, Eric F Bell, Blair C Conn, Thomas J. L de Boer, Robert A Gruendl, Matteo Monelli, Ricardo R Munoz, Abhijit Saha, A. Katherina Vivas, Edouard Bernard, Gurtina Besla, Julio A Carballo-Bello, Antonio Dorta, David Martinez-Delgado, Alex Goater, Vadim Rusakov, Guy S Stringfellow (2020)The Second Data Release of the Survey of the MAgellanic Stellar History (SMASH), In: The Astronomical journal161(2)74 IOP

The Large and Small Magellanic Clouds (LMC and SMC) are the largest satellite galaxies of the Milky Way and close enough to allow for a detailed exploration of their structure and formation history. The Survey of the MAgellanic Stellar History (SMASH) is a community Dark Energy Camera (DECam) survey of the Magellanic Clouds using ~50 nights to sample over ~2400 deg2 centered on the Clouds at ~20% filling factor (but with contiguous coverage in the central regions) and to depths of ~24th mag in ugriz. The primary goals of SMASH are to map out the extended stellar peripheries of the Clouds and uncover their complicated interaction and accretion history as well as to derive spatially resolved star formation histories of the central regions and create a "movie" of their past star formation. Here we announce the second SMASH public data release (DR2), which contains all 197 fully calibrated DECam fields including the main body fields in the central regions. The DR2 data are available through the Astro Data Lab hosted by the NSF's National Optical-Infrared Astronomy Research Laboratory. We highlight three science cases that make use of the SMASH DR2 data and will be published in the future: (1) preliminary star formation histories of the LMC, (2) the search for Magellanic star clusters using citizen scientists, and, (3) photometric metallicities of Magellanic Cloud stars using the DECam u-band.

Randa S. Asa'd, Alexandre Vazdekis, Miguel Cerviño, Noelia Noel, Michael A. Beasley, Mahmoud Kassab (2017)Young LMC clusters: the role of red supergiants and multiple stellar populations in their integrated light and CMDs, In: Monthly Notices of the Royal Astronomical Society471(3)pp. 3599-3614 Oxford University Press

The optical integrated spectra of three Large Magellanic Cloud young stellar clusters (NGC 1984, NGC 1994 and NGC 2011) exhibit concave continua and prominent molecular bands which deviate significantly from the predictions of single stellar population (SSP) models. In order to understand the appearance of these spectra, we create a set of young stellar population (MILES) models, which we make available to the community. We use archival International Ultraviolet Explorer integrated UV spectra to independently constrain the cluster masses and extinction, and rule out strong stochastic effects in the optical spectra. In addition, we also analyse deep colour–magnitude diagrams of the clusters to provide independent age determinations based on isochrone fitting. We explore hypotheses, including age spreads in the clusters, a top-heavy initial mass function, different SSP models and the role of red supergiant stars (RSG). We find that the strong molecular features in the optical spectra can be only reproduced by modelling an increased fraction of about ∼20 per cent by luminosity of RSG above what is predicted by canonical stellar evolution models. Given the uncertainties in stellar evolution at Myr ages, we cannot presently rule out the presence of Myr age spreads in these clusters. Our work combines different wavelengths as well as different approaches (resolved data as well as integrated spectra for the same sample) in order to reveal the complete picture. We show that each approach provides important information but in combination we can better understand the cluster stellar populations.

Ricardo Carrera, Blair C. Conn, Noelia Noel, Justin Read, Ángel R López Sánchez (2017)The Magellanic Inter-Cloud Project (MAGIC) III: First spectroscopic evidence of a dwarf stripping a dwarf, In: Monthly Notices of the Royal Astronomical Society471(4)pp. 4571-4578 Oxford University Press

The Magellanic Bridge (MB) is a gaseous stream that links the Large (LMC) and Small (SMC) Magellanic Clouds. Current simulations suggest that the MB forms from a recent interaction between the Clouds. In this scenario, the MB should also have an associated stellar bridge formed by stars tidally stripped from the SMC by the LMC. There are several observational evidences for these stripped stars, from the presence of intermediate age populations in the MB and carbon stars, to the recent observation of an over-density of RR Lyrae stars offset from the MB. However, spectroscopic confirmation of stripped stars in the MB remains lacking. In this paper, we use medium resolution spectra to derive the radial velocities and metallicities of stars in two fields along the MB. We show from both their chemistry and kinematics that the bulk of these stars must have been tidally stripped from the SMC. This is the first spectroscopic evidence for a dwarf galaxy being tidally stripped by a larger dwarf.

Michele De Leo, Ricardo Carrera, Noelia E.D Noel, Justin I. Read, Denis Erkal, Carme Gallart (2020)Revealing the tidal scars of the Small Magellanic Cloud, In: Monthly Notices of the Royal Astronomical Society495(1)pp. 98-113 Oxford University Press (OUP)

Due to their close proximity, the Large and Small Magellanic Clouds (LMC/SMC) provide natural laboratories for understanding how galaxies form and evolve. With the goal of determining the structure and dynamical state of the SMC, we present new spectroscopic data for ∼3000 SMC red giant branch stars observed using the AAOmega spectrograph at the Anglo-Australian Telescope. We complement our data with further spectroscopic measurements from previous studies that used the same instrumental configuration as well as proper motions from the Gaia Data Release 2 catalogue. Analysing the photometric and stellar kinematic data, we find that the SMC centre of mass presents a conspicuous offset from the velocity centre of its associated H i gas, suggesting that the SMC gas is likely to be far from dynamical equilibrium. Furthermore, we find evidence that the SMC is currently undergoing tidal disruption by the LMC within 2 kpc of the centre of the SMC, and possibly all the way into the very core. This is revealed by a net outward motion of stars from the SMC centre along the direction towards the LMC and an apparent tangential anisotropy at all radii. The latter is expected if the SMC is undergoing significant tidal stripping, as we demonstrate using a suite of N-body simulations of the SMC/LMC system disrupting around the Milky Way. Our results suggest that dynamical models for the SMC that assume a steady state will need to be revisited.

David L. Nidever, Knut Olsen, Alistair R. Walker, A. Katherina Vivas, Robert D. Blum, Catherine Kaleida, Yumi Choi, Blair C. Conn, Robert A. Gruendl, Eric F. Bell, Gurtina Besla, Ricardo R. Muñoz, Carme Gallart, Nicolas F. Martin, Edward W. Olszewski, Abhijit Saha, Antonela Monachesi, Matteo Monelli, Thomas J. L. de Boer, L. Clifton Johnson, Dennis Zaritsky, Guy S. Stringfellow, Roeland P. van der Marel, Maria-Rosa L. Cioni, Shoko Jin, Steven R. Majewski, David Martinez-Delgado, Lara Monteagudo, Noelia Noel, Edouard J. Bernard, Andrea Kunder, You-Hua Chu, Cameron P. M. Bell, Felipe Santana, Joshua Frechem, Gustavo E. Medina, Vaishali Parkash, J. C. Serón Navarrete, Christian Hayes (2017)SMASH: Survey of the MAgellanic Stellar History, In: The Astronomical Journal154(5) IOP Publishing

The Large and Small Magellanic Clouds are unique local laboratories for studying the formation and evolution of small galaxies in exquisite detail. The Survey of the MAgellanic Stellar History (SMASH) is an NOAO community Dark Energy Camera (DECam) survey of the Clouds mapping 480 deg2 (distributed over ~2400 square degrees at ~20% filling factor) to ~24th mag in ugriz. The primary goals of SMASH are to identify low surface brightness stellar populations associated with the stellar halos and tidal debris of the Clouds, and to derive spatially resolved star formation histories. Here, we present a summary of the survey, its data reduction, and a description of the first public Data Release (DR1). The SMASH DECam data have been reduced with a combination of the NOAO Community Pipeline, the PHOTRED automated point-spread-function photometry pipeline, and custom calibration software. The astrometric precision is ~15 mas and the accuracy is ~2 mas with respect to the Gaia reference frame. The photometric precision is ~0.5%–0.7% in griz and ~1% in u with a calibration accuracy of ~1.3% in all bands. The median 5σ point source depths in ugriz are 23.9, 24.8, 24.5, 24.2, and 23.5 mag. The SMASH data have already been used to discover the Hydra II Milky Way satellite, the SMASH 1 old globular cluster likely associated with the LMC, and extended stellar populations around the LMC out to R ~ 18.4 kpc. SMASH DR1 contains measurements of ~100 million objects distributed in 61 fields. A prototype version of the NOAO Data Lab provides data access and exploration tools.

A. Drlica-Wagner, K. Bechtol, S. Allam, D.L. Tucker, R.A. Gruendl, M.D. Johnson, A.R. Walker, D.J. James, D.L. Nidever, K.A.G. Olsen, R.H. Wechsler, M.R.L. Cioni, B.C. Conn, K. Kuehn, T.S. Li, Y.-Y. Mao, N.F. Martin, E. Neilsen, Noelia Noel, A. Pieres, J.D. Simon, G.S. Stringfellow, R.P. van der Marel, B. Yanny (2016)An Ultra-faint Galaxy Candidate Discovered in Early Data from the Magellanic Satellites Survey, In: The Astrophysical Journal833(L5) The American Astronomical Society

We report a new ultra-faint stellar system found in Dark Energy Camera data from the first observing run of the Magellanic Satellites Survey (MagLiteS). MagLiteS J0644−5953 (Pictor II or Pic II) is a low surface brightness (N 28.5 mag arcsec 1 1 2 within its half-light radius) resolved overdensity of old and metal-poor stars located at a heliocentric distance of 45 kpc 4 5 . The physical size ( r1 2 46 pc 11 15 ) and low luminosity ( M V 3.2 mag 0.5 0.4 ) of this satellite are consistent with the locus of spectroscopically confirmed ultra-faint galaxies. MagLiteS J0644−5953 (Pic II) is located 11.3 kpc 0.9 3.1 from the Large Magellanic Cloud (LMC), and comparisons with simulation results in the literature suggest that this satellite was likely accreted with the LMC. The close proximity of MagLiteS J0644−5953 (Pic II) to the LMC also makes it the most likely ultra-faint galaxy candidate to still be gravitationally bound to the LMC.

Nicolas F. Martin, Valentin Jungbluth, David L. Nidever, Eric F. Bell, Gurtina Besla, Robert D. Blum, Maria-Rosa L. Cioni, Blair C. Conn, Catherine C. Kaleida, Carme Gallart, Shoko Jin, Steven R. Majewski, David Martinez-Delgado, Antonela Monachesi, Ricardo R. Muñoz, Noelia Noel, Knut Olsen, Guy S. Stringfellow, Roeland P. van der Marel, A. Katherina Vivas, Alistair R. Walker, Dennis Zaritsky (2016)SMASH 1: A Very Faint Globular Cluster Disrupting in the Outer Reaches of the LMC?, In: Letters of the Astrophysical Journal830(L10) American Astronomical Society

We present the discovery of a very faint stellar system, SMASH 1, that is potentially a satellite of the Large Magellanic Cloud. Found within the Survey of the Magellanic Stellar History (SMASH), SMASH 1 is a compact (${r}_{h}={9.1}_{-3.4}^{+5.9}____,____mathrm{pc}$) and very low luminosity (${M}_{V}=-1.0____pm 0.9$, ${L}_{V}={10}^{2.3____pm 0.4}____,{L}_{____odot }$) stellar system that is revealed by its sparsely populated main sequence and a handful of red giant branch candidate member stars. The photometric properties of these stars are compatible with a metal-poor ($[____mathrm{Fe}/{____rm{H}}]=-2.2$) and old (13 Gyr) isochrone located at a distance modulus of ~18.8, i.e., a distance of $____sim 57____,____mathrm{kpc}$. Situated at 11fdg3 from the LMC in projection, its three-dimensional distance from the Cloud is $____sim 13____,____mathrm{kpc}$, consistent with a connection to the LMC, whose tidal radius is at least $16____,____mathrm{kpc}$. Although the nature of SMASH 1 remains uncertain, its compactness favors it being a stellar cluster and hence dark-matter free. If this is the case, its dynamical tidal radius is only $____lesssim 19____,____mathrm{pc}$ at this distance from the LMC, and smaller than the system's extent on the sky. Its low luminosity and apparent high ellipticity ($____epsilon ={0.62}_{-0.21}^{+0.17}$) with its major axis pointing toward the LMC may well be the tell-tale sign of its imminent tidal demise.

Pol Massana, Noelia E D Noël, David L Nidever, Denis Erkal, Thomas J L de Boer, Yumi Choi, Steven R Majewski, Knut Olsen, Antonela Monachesi, Carme Gallart, Roeland P van der Marel, Tomás Ruiz-Lara, Dennis Zaritsky, Nicolas F Martin, Ricardo R Muñoz, Maria-Rosa L Cioni, Cameron P M Bell, Eric F Bell, Guy S Stringfellow, Vasily Belokurov, Matteo Monelli, Alistair R Walker, David Martínez-Delgado, A Katherina Vivas, Blair C Conn (2020)SMASHing the low surface brightness SMC, In: Monthly Notices of the Royal Astronomical Society498(1)pp. 1034-1049 Oxford University Press

The periphery of the Small Magellanic Cloud (SMC) can unlock important information regarding galaxy formation and evolution in interacting systems. Here, we present a detailed study of the extended stellar structure of the SMC using deep colour–magnitude diagrams, obtained as part of the Survey of the MAgellanic Stellar History (SMASH). Special care was taken in the decontamination of our data from Milky Way (MW) foreground stars, including from foreground globular clusters NGC 362 and 47 Tuc. We derived the SMC surface brightness using a ‘conservative’ approach from which we calculated the general parameters of the SMC, finding a staggered surface brightness profile. We also traced the fainter outskirts by constructing a stellar density profile. This approach, based on stellar counts of the oldest main-sequence turn-off stars, uncovered a tidally disrupted stellar feature that reaches as far out as 12 deg from the SMC centre. We also serendipitously found a faint feature of unknown origin located at ∼14 deg from the centre of the SMC and that we tentatively associated with a more distant structure. We compared our results to in-house simulations of a 1 × 109 M⊙ SMC, finding that its elliptical shape can be explained by its tidal disruption under the combined presence of the MW and the Large Magellanic Cloud. Finally, we found that the older stellar populations show a smooth profile while the younger component presents a jump in the density followed by a flat profile, confirming the heavily disturbed nature of the SMC.

A. Pieres, B. X. Santiago, A. Drlica-Wagner, K. Bechtol, R. P. van der Marel, G. Besla, N. F. Martin, V. Belokurov, C. Gallart, D. Martinez-Delgado, J. Marshall, Noelia Noel, S. R. Majewski, M.-R. L. Cioni, T. S. Li, W. Hartley, E. Luque, B. C. Conn, A. R. Walker, Eduardo Balbinot, G. S. Stringfellow, K. A. G. Olsen, D. Nidever, L. N. da Costa, R. Ogando, M. Maia, A. Fausti Neto, T. M. C. Abbott, F. B. Abdalla, S. Allam, J. Annis, A. Benoit-Lévy, A. Carnero Rosell, M. Carrasco Kind, J. Carretero, C. E. Cunha, C. B. D'Andrea, S. Desai, H. T. Diehl, P. Doel, B. Flaugher, P. Fosalba, J. García-Bellido, D. Gruen, R. A. Gruendl, J. Gschwend, G. Gutierrez, K. Honscheid, D. James, K. Kuehn, N. Kuropatkin, F. Menanteau, R. Miquel, A. A. Plazas, A. K. Romer, M. Sako, E. Sanchez, V. Scarpine, M. Schubnell, I. Sevilla-Noarbe, R. C. Smith, M. Soares-Santos, F. Sobreira, E. Suchyta, M. E. C. Swanson, G. Tarle, D. L. Tucker, W. Wester (2017)A stellar overdensity associated with the Small Magellanic Cloud, In: Monthly Notices of the Royal Astronomical Society468(2)pp. 1349-1360 Oxford University Press

We report the discovery of a stellar overdensity 8° north of the centre of the Small Magellanic Cloud (SMC; Small Magellanic Cloud Northern Over-Density; SMCNOD), using data from the first 2 yr of the Dark Energy Survey (DES) and the first year of the MAGellanic SatelLITEs Survey (MagLiteS). The SMCNOD is indistinguishable in age, metallicity and distance from the nearby SMC stars, being primarily composed of intermediate-age stars (6 Gyr, Z=0.001), with a small fraction of young stars (1 Gyr, Z=0.01). The SMCNOD has an elongated shape with an ellipticity of 0.6 and a size of ∼ 6° × 2°. It has an absolute magnitude of MV ≅ −7.7, rh = 2.1 kpc, and μV(r < rh) = 31.2 mag arcsec−2. We estimate a stellar mass of ∼105 M⊙, following a Kroupa mass function. The SMCNOD was probably removed from the SMC disc by tidal stripping, since it is located near the head of the Magellanic Stream, and the literature indicates likely recent Large Magellanic Cloud-SMC encounters. This scenario is supported by the lack of significant H I gas. Other potential scenarios for the SMCNOD origin are a transient overdensity within the SMC tidal radius or a primordial SMC satellite in advanced stage of disruption.