arXiv subjects

L. Santana-Silva

Publications and source records attributed to L. Santana-Silva.

24 records · Page 2Linked to original sources

arXiv2021

Two Ultra-Faint Milky Way Stellar Systems Discovered in Early Data from the DECam Local Volume Exploration Survey

We report the discovery of two ultra-faint stellar systems found in early data from the DECam Local Volume Exploration survey (DELVE). The first system, Centaurus I (DELVE J1238-4054), is identified as a resolved overdensity of old and metal-poor stars with a heliocentric distance of ${\rm D}_{\odot} = 116.3_{-0.6}^{+0.6}$ kpc, a half-light radius of $r_h = 2.3_{-0.3}^{+0.4}$ arcmin, an age of $τ> 12.85$ Gyr, a metallicity of $Z = 0.0002_{-0.0002}^{+0.0001}$, and an absolute magnitude of $M_V = -5.55_{-0.11}^{+0.11}$ mag. This characterization is consistent with the population of ultra-faint satellites, and confirmation of this system would make Centaurus I one of the brightest recently discovered ultra-faint dwarf galaxies. Centaurus I is detected in Gaia DR2 with a clear and distinct proper motion signal, confirming that it is a real association of stars distinct from the Milky Way foreground; this is further supported by the clustering of blue horizontal branch stars near the centroid of the system. The second system, DELVE 1 (DELVE J1630-0058), is identified as a resolved overdensity of stars with a heliocentric distance of ${\rm D}_{\odot} = 19.0_{-0.6}^{+0.5} kpc$, a half-light radius of $r_h = 0.97_{-0.17}^{+0.24}$ arcmin, an age of $τ= 12.5_{-0.7}^{+1.0}$ Gyr, a metallicity of $Z = 0.0005_{-0.0001}^{+0.0002}$, and an absolute magnitude of $M_V = -0.2_{-0.6}^{+0.8}$ mag, consistent with the known population of faint halo star clusters. Given the low number of probable member stars at magnitudes accessible with Gaia DR2, a proper motion signal for DELVE 1 is only marginally detected. We compare the spatial position and proper motion of both Centaurus I and DELVE 1 with simulations of the accreted satellite population of the Large Magellanic Cloud (LMC) and find that neither is likely to be associated with the LMC.

astro-ph.GA↗

arXiv2020

Discovery of an Ultra-Faint Stellar System near the Magellanic Clouds with the DECam Local Volume Exploration (DELVE) Survey

We report the discovery of a new ultra-faint stellar system found near the Magellanic Clouds in the DECam Local Volume Exploration (DELVE) Survey. This new system, DELVE J0155$-$6815 (DELVE 2), is located at a heliocentric distance of $D_{\odot} = 71 \pm 4\text{ kpc}$, which places it at a 3D physical separation of 12 kpc from the center of Small Magellanic Cloud (SMC) and 28 kpc from the center of the Large Magellanic Cloud (LMC). DELVE 2 is identified as a resolved overdensity of old ($τ> 13.3\text{ Gyr}$) and metal-poor (${\rm [Fe/H]} = -2.0_{-0.5}^{+0.2}$ dex) stars with a projected half-light radius of $r_{1/2} = 21^{+4}_{-3}\text{ pc}$ and an absolute magnitude of $M_V = -2.1^{+0.4}_{-0.5}\text{ mag}$. The size and luminosity of DELVE 2 are consistent with both the population of recently discovered ultra-faint globular clusters and the smallest ultra-faint dwarf galaxies. However, its age and metallicity would place it among the oldest and most metal-poor globular clusters in the Magellanic system. DELVE 2 is detected in Gaia DR2 with a clear proper motion signal, with multiple blue horizontal branch stars near the centroid of the system with proper motions consistent with the systemic mean. We measure the system proper motion to be $(μ_α \cos δ, μ_δ)= (1.02_{-0.25}^{+0.24}, -0.85_{-0.19}^{+0.18})$ mas yr$^{-1}$. We compare the spatial position and proper motion of DELVE 2 with simulations of the accreted satellite population of the LMC and find that it is very likely to be associated with the LMC.

astro-ph.GA↗

arXiv2020

A DESGW Search for the Electromagnetic Counterpart to the LIGO/Virgo Gravitational Wave Binary Neutron Star Merger Candidate S190510g

We present the results from a search for the electromagnetic counterpart of the LIGO/Virgo event S190510g using the Dark Energy Camera (DECam). S190510g is a binary neutron star (BNS) merger candidate of moderate significance detected at a distance of 227$\pm$92 Mpc and localized within an area of 31 (1166) square degrees at 50\% (90\%) confidence. While this event was later classified as likely non-astrophysical in nature within 30 hours of the event, our short latency search and discovery pipeline identified 11 counterpart candidates, all of which appear consistent with supernovae following offline analysis and spectroscopy by other instruments. Later reprocessing of the images enabled the recovery of 6 more candidates. Additionally, we implement our candidate selection procedure on simulated kilonovae and supernovae under DECam observing conditions (e.g., seeing, exposure time) with the intent of quantifying our search efficiency and making informed decisions on observing strategy for future similar events. This is the first BNS counterpart search to employ a comprehensive simulation-based efficiency study. We find that using the current follow-up strategy, there would need to be 19 events similar to S190510g for us to have a 99\% chance of detecting an optical counterpart, assuming a GW170817-like kilonova. We further conclude that optimization of observing plans, which should include preference for deeper images over multiple color information, could result in up to a factor of 1.5 reduction in the total number of followups needed for discovery.

astro-ph.HE↗

arXiv2020

The Environment of Lyman Break Analogues (ELBA) survey: Star-forming galaxies in small groups

The Environment of Lyman Break Analogues (ELBA) survey is an imaging survey of 33 $deg^{2}$ of the southern sky. The survey was observed in {\it u}, {\it g}, {\it r}, and {\it i} bands with the Dark Energy Camera (DECam) on the Blanco telescope. The main goal of this project is to investigate the environment of Lyman break analogues (LBAs), low-redshift (z $\sim $0.2) galaxies that are remarkably similar to typical star-forming galaxies at z $\sim$ 3. We explore whether the environment has any influence on the observed properties of these galaxies, providing valuable insight on the formation and evolution of galaxies over cosmic time. Using the Nearest Neighbour method, we measure the local density of each object ranging from small to large scales (clusters of galaxies). Comparing the environment around LBAs with that of the general galaxy population in the field, we conclude that LBAs, on average, populate denser regions at small scales ($\sim$ $1.5Mpc$), but are located in similar environment to other star-forming galaxies at larger scales ($\sim$ $3.0 Mpc$). This offers evidence that nearby encounters such as mergers may influence the star formation activity in LBAs, before infall onto larger galaxy clusters. We interpret this an indication of galaxy preprocessing, in agreement with theoretical expectations for galaxies at z $\sim$ 2 -3 where the gravitational interactions are more intense in early formation processes of this objects

astro-ph.GA↗

arXiv2019

Assessing the photometric redshift precision of the S-PLUS survey: the Stripe-82 as a test-case

In this paper we present a thorough discussion about the photometric redshift (photo-z) performance of the Southern Photometric Local Universe Survey (S-PLUS). This survey combines a 7 narrow + 5 broad passband filter system, with a typical photometric-depth of r$\sim$21 AB. For this exercise, we utilize the Data Release 1 (DR1), corresponding to 336 deg$^{2}$ from the Stripe-82 region. We rely on the \texttt{BPZ2} code to compute our estimates, using a new library of SED models, which includes additional templates for quiescent galaxies. When compared to a spectroscopic redshift control sample of $\sim$100k galaxies, we find a precision of $σ_{z}<$0.8\%, $<$2.0\% or $<$3.0\% for galaxies with magnitudes r$<$17, $<$19 and $<$21, respectively. A precision of 0.6\% is attained for galaxies with the highest \texttt{Odds} values. These estimates have a negligible bias and a fraction of catastrophic outliers inferior to 1\%. We identify a redshift window (i.e., 0.26$<z<$0.32) where our estimates double their precision, due to the simultaneous detection of two emission-lines in two distinct narrow-bands; representing a window opportunity to conduct statistical studies such as luminosity functions. We forecast a total of $\sim$2M, $\sim$16M and $\sim$32M galaxies in the S-PLUS survey with a photo-z precision of $σ_{z}<$1.0\%, $<$2.0\% and $<$2.5\% after observing 8000 $deg^{2}$. We also derive redshift Probability Density Functions, proving their reliability encoding redshift uncertainties and their potential recovering the $n(z)$ of galaxies at $z<0.4$, with an unprecedented precision for a photometric survey in the southern hemisphere.

astro-ph.GA↗

arXiv2019

A faint halo star cluster discovered in the Blanco Imaging of the Southern Sky Survey

We present the discovery of a faint, resolved stellar system, BLISS J0321+0438 (BLISS 1), found in Dark Energy Camera data from the first observing run of the Blanco Imaging of the Southern Sky (BLISS) Survey. BLISS J0321+0438 (BLISS 1) is located at (RA, Dec) = (177.511, -41.772) deg with a heliocentric distance of D = 23.7$^{+1.9}_{-1.0}$ kpc. It is a faint, Mv = 0.0$^{+1.7}_{-0.7}$ mag, and compact, rh = 4.1 +/- 1 pc, system consistent with previously discovered faint halo star clusters. Using data from the second data release of the Gaia satellite, we measure a proper motion of $(μ_α\cos δ, μ_δ)$ = (-2.37 +/- 0.06, 0.16 +/- 0.04) mas/yr. Combining the available positional and velocity information with simulations of the accreted satellite population of the Large Magellanic Cloud, we find that it is unlikely that BLISS J0321+0438 (BLISS 1) originated with the Large Magellanic Cloud.

astro-ph.GA↗