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Ultrafaint Dwarf Galaxy Candidates in the M81 Group: Signatures of Group Accretion
The faint and ultrafaint dwarf galaxies in the Local Group form the observational bedrock upon which our understanding of small-scale cosmology rests. In order to understand whether this insight generalizes, it is imperative to use resolved-star techniques to discover similarly faint satellites in nearby galaxy groups. We describe our search for ultrafaint galaxies in the M81 group using deep ground-based resolved-star data sets from Subaruâs Hyper Suprime-Cam. We present one new ultrafaint dwarf galaxy in the M81 group and identify five additional extremely low surface brightness candidate ultrafaint dwarfs that reach deep into the ultrafaint regime to M V ⌠â 6 (similar to current limits for Andromeda satellites). These candidatesâ luminosities and sizes are similar to known Local Group dwarf galaxies Tucana B, Canes Venatici I, Hercules, and Boötes I. Most of these candidates are likely to be real, based on tests of our techniques on blank fields. Intriguingly, all of these candidates are spatially clustered around NGC 3077, which is itself an M81 group satellite in an advanced state of tidal disruption. This is somewhat surprising, as M81 itself and its largest satellite M82 are both substantially more massive than NGC 3077 and, by virtue of their greater masses, would have been expected to host as many or more ultrafaint candidates. These results lend considerable support to the idea that satellites of satellites are an important contribution to the growth of satellite populations around Milky Way-mass galaxies
Ultrafaint Dwarf Galaxy Candidates in the M81 Group: Signatures of Group Accretion
The faint and ultrafaint dwarf galaxies in the Local Group form the
observational bedrock upon which our understanding of small-scale cosmology
rests. In order to understand whether this insight generalizes, it is
imperative to use resolved-star techniques to discover similarly faint
satellites in nearby galaxy groups. We describe our search for ultrafaint
galaxies in the M81 group using deep ground-based resolved-star data sets from
Subaru's Hyper Suprime-Cam. We present one new ultrafaint dwarf galaxy in the
M81 group and identify five additional extremely low surface brightness
candidate ultrafaint dwarfs that reach deep into the ultrafaint regime to (similar to current limits for Andromeda satellites). These
candidates' luminosities and sizes are similar to known Local Group dwarf
galaxies Tucana B, Canes Venatici I, Hercules, and Bo\"otes I. Most of these
candidates are likely to be real, based on tests of our techniques on blank
fields. Intriguingly, all of these candidates are spatially clustered around
NGC 3077, which is itself an M81 group satellite in an advanced state of tidal
disruption. This is somewhat surprising, as M81 itself and its largest
satellite M82 are both substantially more massive than NGC 3077 and by virtue
of their greater masses, would have been expected to host as many or more
ultrafaint candidates. These results lend considerable support to the idea that
satellites of satellites are an important contribution to the growth of
satellite populations around Milky Way-mass galaxies.Comment: The Astrophysical Journal Letters; in press. 11 pages, 4 figures, 1
tabl
Improving Undergraduate Astronomy Students' Skills with Research Literature via Accessible Summaries: A Case Study with Astrobites-based Lesson Plans
Undergraduate physics and astronomy students are expected to engage with
scientific literature as they begin their research careers, but reading
comprehension skills are rarely explicitly taught in major courses. We seek to
determine the efficacy of lesson plans designed to improve undergraduate
astronomy (or related) majors' perceived ability to engage with research
literature by using accessible summaries of current research written by experts
in the field. During the 2022-2023 academic year, twelve faculty members
incorporated lesson plans using accessible summaries from Astrobites into their
undergraduate astronomy major courses, surveyed their students before and after
the activities, and participated in follow-up interviews with our research
team. Quantitative and qualitative survey data clearly show that students'
perceptions of their abilities with jargon, identifying main takeaways of a
paper, conceptual understanding of physics and astronomy, and communicating
scientific results all improved with use of the tested lesson plans.
Additionally, students show evidence of increased confidence of their abilities
within astronomy after exposure to these lessons, and instructors valued a
ready-to-use resource to incorporate reading comprehension in their pedagogy.
This case study with Astrobites-based lesson plans suggests that incorporating
current research in the undergraduate classroom through accessible literature
summaries may increase students' confidence and ability to engage with research
literature, as well as their preparation for participation in research and
applied careers.Comment: Submitted to PRPE
COOL-LAMPS III: Discovery of a 25".9 Separation Quasar Lensed by a Merging Galaxy Cluster
In the third paper from the COOL-LAMPS Collaboration, we report the discovery
of COOL J0542-2125, a gravitationally lensed quasar at , observed as
three images due to an intervening massive galaxy cluster at . The
lensed quasar images were identified in a search for lens systems in recent
public optical imaging data and have separations on the sky up to 25".9, wider
than any previously known lensed quasar. The galaxy cluster acting as a strong
lens appears to be in the process of merging, with two sub-clusters separated
by Mpc in the plane of the sky, and their central galaxies showing a
radial velocity difference of km/s. Both cluster cores show
strongly lensed images of an assortment of background sources, as does the
region between them. A preliminary strong lens model implies masses of $M(<250\
\rm{kpc}) = 1.79^{+0.16} _{-0.01} \times 10^{14} M_{\odot}M(<250\
\rm{kpc}) = 1.48^{+0.04}_{-0.10} \times 10^{14} M_{\odot}$ for the East and
West sub-clusters, respectively. This line of sight is also coincident with a
ROSAT ALL-sky Survey source, centered between the two confirmed cluster halos
reminiscent of other major cluster-scale mergers.Comment: 13 pages, 6 figures. Submitted to Ap
COOL-LAMPS. VI. Lens Model and New Constraints on the Properties of COOL J1241+2219, a Bright z = 5 Lyman Break Galaxy and its z = 1 Cluster Lens
We present a strong lensing analysis of COOL J1241+2219, the brightest known gravitationally lensed galaxy at z â„ 5, based on new multiband Hubble Space Telescope (HST) imaging data. The lensed galaxy has a redshift of z = 5.043, placing it shortly after the end of the âEpoch of Reionization,â and an AB magnitude z AB = 20.47 mag (Khullar et al.). As such, it serves as a touchstone for future research of that epoch. The high spatial resolution of HST reveals internal structure in the giant arc, from which we identify 15 constraints and construct a robust lens model. We use the lens model to extract the cluster mass and lensing magnification. We find that the mass enclosed within the Einstein radius of the z = 1.001 cluster lens is M(<5.âł77)=1.079â0.007+0.023Ă1013Mâ , significantly lower than other known strong lensing clusters at its redshift. The average magnification of the giant arc is ăÎŒ arcă = 76â20+40 , a factor of 2.4â0.7+1.4 greater than previously estimated from ground-based data; the flux-weighted average magnification is ăÎŒ arcă = 92â31+37 . We update the current measurements of the stellar mass and star formation rate (SFR) of the source for the revised magnification to log(Mâ/Mâ)= 9.7 ± 0.3 and SFR = 10.3â4.4+7.0 M â yrâ1, respectively. The powerful lensing magnification acting upon COOL J1241+2219 resolves the source and enables future studies of the properties of its star formation on a clump-by-clump basis. The lensing analysis presented here will support upcoming multiwavelength characterization with HST and JWST data of the stellar mass assembly and physical properties of this high-redshift lensed galaxy
COOL-LAMPS VI: Lens model and New Constraints on the Properties of COOL J1241+2219, a Bright z = 5 Lyman Break Galaxy and its z = 1 Cluster Lens
We present a strong lensing analysis of COOL J1241+2219, the brightest known
gravitationally lensed galaxy at , based on new multi-band Hubble
Space Telescope (HST) imaging data. The lensed galaxy has a redshift of
z=5.043, placing it shortly after the end of the Epoch of Reionization, and an
AB magnitude z_AB=20.47 mag (Khullar et al. 2021). As such, it serves as a
touchstone for future research of that epoch. The high spatial resolution of
HST reveals internal structure in the giant arc, from which we identify 15
constraints and construct a robust lens model. We use the lens model to extract
cluster mass and lensing magnification. We find that the mass enclosed within
the Einstein radius of the z=1.001 cluster lens is
M(<5.77'')=, significantly lower than other known
strong lensing clusters at its redshift. The average magnification of the giant
arc is , a factor of greater
than previously estimated from ground-based data; the flux-weighted average
magnification is We update the current
measurements of the stellar mass and star formation rate (SFR) of the source
for the revised magnification, and yr. The powerful lensing
magnification acting upon COOL J1241+2219 resolves the source and enables
future studies of the properties of its star formation on a clump-by-clump
basis. The lensing analysis presented here will support upcoming
multiwavelength characterization with HST and JWST data of the stellar mass
assembly and physical properties of this high-redshift lensed galaxy.Comment: Submitted to Ap
COOL-LAMPS. IV. A Sample of Bright Strongly Lensed Galaxies at 3 < z < 4
We report the discovery of five bright, strong gravitationally lensed galaxies at 3 < z < 4: COOL J0101+2055 (z = 3.459), COOL J0104â0757 (z = 3.480), COOL J0145+1018 (z = 3.310), COOL J0516â2208 (z = 3.549), and COOL J1356+0339 (z = 3.753). These galaxies have magnitudes of rAB, zAB < 21.81 mag and are lensed by galaxy clusters at 0.26 < z < 1. This sample nearly doubles the number of known bright lensed galaxies with extended arcs at 3 < z < 4. We characterize the lensed galaxies using ground-based grz/giy imaging and optical spectroscopy. We report model-based magnitudes and derive stellar masses, dust content, and star formation rates via stellar population synthesis modeling. Building lens models based on ground-based imaging, we estimate source magnifications ranging from âŒ29 to âŒ180. Combining these analyses, we derive demagnified stellar masses in the range and star formation rates in the youngest age bin in the range , placing the sample galaxies on the massive end of the star-forming main sequence in this redshift interval. In addition, three of the five galaxies have strong Lyα emissions, offering unique opportunities to study Lyα emitters at high redshift in future work
COOL-LAMPS. VII. Quantifying Strong-lens Scaling Relations with 177 Cluster-scale Gravitational Lenses in DECaLS
We compute parametric measurements of the Einstein-radius-enclosed total mass
for 177 cluster-scale strong gravitational lenses identified by the ChicagO
Optically-selected Lenses Located At the Margins of Public Surveys (COOL-LAMPS)
collaboration with lens redshifts ranging from using only two measured parameters in each lensing system: the Einstein
radius, and the brightest-cluster-galaxy (BCG) redshift. We then constrain the
Einstein-radius-enclosed luminosity and stellar mass by fitting parametric
spectral energy distributions (SEDs) with aperture photometry from the Dark
Energy Camera Legacy Survey (DECaLS) in the , , and -band Dark Energy
Camera (DECam) filters. We find that the BCG redshift, enclosed total mass, and
enclosed luminosity are strongly correlated and well described by a planar
relationship in 3D space. We also find that the enclosed total mass and stellar
mass are correlated with a logarithmic slope of , and the
enclosed total mass and stellar-to-total mass fraction are correlated with a
logarithmic slope of . The correlations described here can be
used to validate strong lensing candidates in upcoming imaging surveys -- such
as Rubin/Legacy Survey of Space and Time (LSST) -- in which an algorithmic
treatment of lensing systems will be needed due to the sheer volume of data
these surveys will produce.Comment: 17 pages, 5 figures, 2 tables. Submitted to The Astrophysical
Journal. v3: updated authors, formatting, grammar, and reference