arXiv subjects

Carl J. Grillmair

Publications and source records attributed to Carl J. Grillmair.

At least 19 recordsLinked to original sources

arXiv2024

The Multiple Extended Tidal Tails of NGC 288

Using photometry and proper motions from Pan-STARRS, DECaLS, and Gaia DR3, we detect a ~35 to 70 degree-long trailing stellar debris stream associated with the globular cluster NGC 288. The trajectory of the trailing tail is not well matched by a model stream evolved in a static Galactic potential, but is reasonably well-matched by a stream modeled in a potential that incorporates a massive, infalling Large Magellanic Cloud. We also detect a broad, at least ~40 degree-long leading tail that appears to be composed of at least two narrower, spatially offset, and kinematically distinct streams. Stream modeling predicts a similar broad composite of streams and suggests that these narrower components could each be made up of one or more generations of tidal tails, each formed during different orbits over the past few gigayears. On the other hand, NGC 288 is believed to have been brought into the Galactic halo during the Gaia-Enceladus-Sausage accretion event, and the tangential velocity dispersions of our stream candidates are indeed most consistent with having been stripped in a parent galaxy that had a large, cored dark matter halo. Tables of the most highly ranked stream star candidates are provided for ongoing and future spectroscopic surveys.

astro-ph.GA↗

arXiv2024

NEOWISE-R Caught the Luminous SN 2023ixf in Messier 101

The reactivated Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE-R) serendipitously caught the Type II supernova SN 2023ixf in Messier 101 on the rise, starting day 3.6 through day 10.9, and on the late-time decline from days 211 through 213 and days 370 through 372. We have considered these mid-infrared (mid-IR) data together with observations from the ultraviolet (UV) through the near-IR, when possible. At day 3.6 we approximated the optical emission with a hot, ~26,630 K blackbody, with a notable UV excess likely from strong SN shock interaction with circumstellar matter (CSM). In the IR, however, a clear excess is also obvious, and we fit it with a cooler, ~1,620 K blackbody with radius of ~2.6 x 10^{15} cm, consistent with dust in the progenitor's circumstellar shell likely heated by the UV emission from the CSM interaction. On day 10.8, the light detected was consistent with SN ejecta-dominated emission. At late times we also observed a clear NEOWISE-R excess, which could arise either from newly formed dust in the inner ejecta or in the contact discontinuity between the forward and reverse shocks, or from more distant pre-existing dust grains in the SN environment. Furthermore, the large 4.6 micron excess at late times can also be explained by the emergence of the carbon monoxide 1--0 vibrational band. SN 2023ixf is the best-observed SN IIP in the mid-IR during the first several days after explosion and one of the most luminous such SNe ever seen.

astro-ph.SR↗

arXiv2022

The Dark Matter Halo of M54

M54 is a prototype of a globular cluster embedded in a dark matter halo. Gaia EDR3 photometry and proper motions separate the old, metal-poor stars from the more metal rich and younger dwarf galaxy stars. The metal poor stars dominate the inner 50 pc, with a velocity dispersion profile that declines to a minimum around 30 pc then rises back to nearly the central velocity dispersion, as expected for a globular cluster at the center of a dark matter halo. The Jeans analysis of the three separate stellar populations give consistent masses that rise approximately linearly with radius to 1 kpc, implying a small core or cuspy halo. These data are compatible with an infalling CDM dark matter halo reduced to 3x10^8 M_sun at the 50 kpc apocenter 2.3 Gyr ago, with a central globular cluster surrounded by the remnant of a dwarf galaxy. Tides gradually remove material beyond 1 kpc but have little effect on the stars and dark matter within 300 pc of the center. M54 appears to be a transitional system between globular clusters with and without local dark halos, whose evolution within the galaxy depends sensitively on the time of accretion and orbital pericenter.

astro-ph.GA↗

arXiv2022

Joint Survey Processing II: Stellar Proper Motions in the COSMOS Field, from Hubble Space Telescope ACS and Subaru Telescope HSC Observations

We analyze stellar proper motions in the COSMOS field to assess the presence of bulk motions. At bright magnitudes (G-band 18.5--20.76 AB), we use the proper motions of 1,010 stars in the Gaia DR2 catalog. At the faint end, we computed proper motions of 11,519 point-like objects at i-band magnitudes 19--25 AB using Hubble ACS and Subaru HSC, which span two epochs about 11 years apart. In order to measure these proper motions with unprecedented accuracy at faint magnitudes, we developed a foundational set of astrometric tools which will be required for Joint Survey Processing (JSP) of data from the next generation of optical/infrared surveys. The astrometric grids of Hubble ACS and Subaru HSC mosaics were corrected at the catalog level, using proper motion-propagated and parallax-corrected Gaia DR2 sources. These astrometric corrections were verified using compact extragalactic sources. Upon comparison of our measured proper motions with Gaia DR2, we estimate the uncertainties in our measurements to be ~2--3 mas/yr per axis, down to 25.5 AB mag. We corrected proper motions for the mean motion of the Sun, and we find that late-type main-sequence stars predominantly in the thin disk in the COSMOS field have space velocities mainly towards the Galactic center. We detect candidate high-velocity (> 220 km/s) stars, 6 of them at ~0.4-6 kpc from the Gaia sample, and 5 of them at ~20 kpc from the faint star HSC and ACS sample. The sources from the faint star sample may be candidate halo members of the Sangarius stream.

astro-ph.GA↗

arXiv2022

The Extended Tidal Tails of NGC 7089 (M2)

Using photometry and proper motions from Gaia Early Data Release 3, we detect a 45 degree-long trailing stellar debris stream associated with the old, metal-poor globular cluster NGC 7089. With a width on the order of 100 pc, the extended stream appears to be as dynamically cold as the coldest known streams found to date. There is some evidence for an extended leading tail extending between 28 and 37 degrees from the cluster, though the greater distance of this tail, combined with proper motions that are virtually indistinguishable from those of foreground stars, make the detection much less certain. The proper motion profile and the path on the sky of the trailing tail are not well matched using a simple Galactic potential comprised purely of a disk, bulge, and spherical halo. However, the addition of a moving, massive (M = 1.88 x 10^(11) solar masses) Large Magellanic Cloud brings the model predictions into much better agreement with the observables. We provide tables of the most highly ranked candidate stream stars for follow-up by ongoing and future spectroscopic surveys.

astro-ph.GA↗

arXiv2022

Estimate of the Mass and Radial Profile of the Orphan-Chenab Stream's Dwarf Galaxy Progenitor Using MilkyWay@home

We fit the mass and radial profile of the Orphan-Chenab Stream's (OCS) dwarf galaxy progenitor by using turnoff stars in the Sloan Digital Sky Survey (SDSS) and the Dark Energy Camera (DEC) to constrain N-body simulations of the OCS progenitor falling into the Milky Way on the 1.5 PetaFLOPS MilkyWay@home distributed supercomputer. We infer the internal structure of the OCS's progenitor under the assumption that it was a spherically symmetric dwarf galaxy comprised of a stellar system embedded in an extended dark matter halo. We optimize the evolution time, the baryonic and dark matter scale radii, and the baryonic and dark matter masses of the progenitor using a differential evolution algorithm. The likelihood score for each set of parameters is determined by comparing the simulated tidal stream to the angular distribution of OCS stars observed in the sky. We fit the total mass of the OCS's progenitor to ($2.0\pm0.3$) $\times 10^7 M_\odot$ with a mass-to-light ratio of $γ=73.5\pm10.6$ and ($1.1\pm0.2$)$\times10^6M_{\odot}$ within 300 pc of its center. Within the progenitor's half-light radius, we estimate total a mass of ($4.0\pm1.0$)$\times10^5M_{\odot}$. We also fit the current sky position of the progenitor's remnant to be $(α,δ)=((166.0\pm0.9)^\circ,(-11.1\pm2.5)^\circ)$ and show that it is gravitationally unbound at the present time. The measured progenitor mass is on the low end of previous measurements, and if confirmed lowers the mass range of ultrafaint dwarf galaxies. Our optimization assumes a fixed Milky Way potential, OCS orbit, and radial profile for the progenitor, ignoring the impact of the Large Magellanic Cloud.

astro-ph.GA↗

arXiv2021

Warm Spitzer IRAC Photometry: dependencies on observing mode and exposure time

We investigate differences in Spitzer/IRAC 3.6 and 4.5micron photometry that depend on observing strategy. Using archival calibration data we perform an in-depth examination of the measured flux densities ("fluxes") of ten calibration stars, observed with all the possible observing strategies. We then quantify differences in the measured fluxes as a function of 1) array mode (full or subarray), 2) exposure time, and 3) dithering versus staring observations. We find that the median fluxes measured for sources observed using the full array are 1.6% and 1% lower than those observed with the subarray at [3.6] and [4.5], respectively. Additionally, we found a dependence on the exposure time such that for [3.6] observations the long frame times are measured to be lower than the short frame times by a median value of 3.4% in full array and 2.9% in subarray. For [4.5] observations the longer frame times are 0.6% and 1.5% in full and subarray respectively. These very small variations will likely only affect science users who require high-precision photometry from multiple different observing modes. We find no statistically significant difference for fluxes obtained with dithered and staring-modes. When considering all stars in the sample, the fractional well depth of the pixel is correlated with the different observed fluxes. We speculate the cause to be a small non-linearity in the pixels at the lowest well depths where deviations from linearity were previously assumed to be negligible.

astro-ph.IM↗

arXiv2021

Testing for Dark Matter in the Outskirts of Globular Clusters

The proper motions of stars in the outskirts of globular clusters are used to estimate cluster velocity dispersion profiles as far as possible within their tidal radii. We use individual color-magnitude diagrams to select high probability cluster stars for 25 metal-poor globular clusters within 20 kpc of the sun, 19 of which have substantial numbers of stars at large radii. Of the 19, 11 clusters have a falling velocity dispersion in the 3-6 half mass radii range, 6 are flat, and 2 plausibly have a rising velocity dispersion. The profiles are all in the range expected from simulated clusters started at high redshift in a zoom-in cosmological simulation. The 11 clusters with falling velocity dispersion profiles are consistent with no dark matter above the Galactic background. The 6 clusters with approximately flat velocity dispersion profiles could have local dark matter, but are ambiguous. The 2 clusters with rising velocity dispersion profiles are consistent with a remnant local dark matter halo, but need membership confirmation and detailed orbital modeling to further test these preliminary results.

astro-ph.GA↗

arXiv2019

Detection of a 50 degree-long Trailing Tidal Tail for the Globular Cluster M5

Using photometry and proper motions from Gaia Data Release 2, we detect a 50 degree-long stream of about 70 stars extending westward from the halo globular cluster M5. Based on the similarities in distance, proper motions, inferred color-magnitude distribution, and trajectory, we identify this stream as the trailing tidal tail of M5. While the surface density of stars is very low (~1.5 stars per square degree, or approximately 35 magnitudes per square arcsecond), selecting only stars having proper motions consistent with the orbit of the cluster yield a detection significance ~10 sigma. While we find a possible continuation of the stream to ~85 degrees, increasing foreground contamination combined with a greater predicted stream distance make it difficult to detect with current data even if the stream continues unabated. The non-uniform distribution of stars in the stream appears to be consistent with episodic tidal stripping, with the most recently shed stars now trailing the cluster by tens of degrees. We provide a table of the highest-ranked candidate stream stars for ongoing and future spectroscopic surveys.

astro-ph.GA↗

arXiv2019

Astrophysical Tests of Dark Matter with Maunakea Spectroscopic Explorer

We discuss how astrophysical observations with the Maunakea Spectroscopic Explorer (MSE), a high-multiplexity (about 4300 fibers), wide field-of-view (1.5 square degree), large telescope aperture (11.25 m) facility, can probe the particle nature of dark matter. MSE will conduct a suite of surveys that will provide critical input for determinations of the mass function, phase-space distribution, and internal density profiles of dark matter halos across all mass scales. N-body and hydrodynamical simulations of cold, warm, fuzzy and self-interacting dark matter suggest that non-trivial dynamics in the dark sector could have left an imprint on structure formation. Analysed within these frameworks, the extensive and unprecedented datasets produced by MSE will be used to search for deviations away from cold and collisionless dark matter model. MSE will provide an improved estimate of the local density of dark matter, critical for direct detection experiments, and will improve estimates of the J-factor for indirect searches through self-annihilation or decay into Standard Model particles. MSE will determine the impact of low mass substructures on the dynamics of Milky Way stellar streams in velocity space, and will allow for estimates of the density profiles of the dark matter halos of Milky Way dwarf galaxies using more than an order of magnitude more tracers. In the low redshift Universe, MSE will provide critical redshifts to pin down the luminosity functions of vast numbers of satellite systems, and MSE will be an essential component of future strong lensing measurements to constrain the halo mass function. Across nearly all mass scales, the improvements offered by MSE, in comparison to other facilities, are such that the relevant analyses are limited by systematics rather than statistics.

astro-ph.CO↗

arXiv2018

LSST Cadence Optimization White Paper in Support of Observations of Unresolved Tidal Stellar Streams in Galaxies beyond the Local Group

Deep observations of faint surface brightness stellar tidal streams in external galaxies with LSST are addressed in this White Paper contribution. We propose using the Wide--Fast--Deep survey that contains several nearby galaxies (at distances where the stars themselves are not resolved, i.e., beyond 20 Mpc). In the context of hierarchical galaxy formation, it is necessary to understand the prevalence and properties of tidal substructure around external galaxies based on integrated (i.e., unresolved) diffuse light. This requires collecting observations on much larger samples of galaxies than the Milky Way and M31. We will compare the observed structures to the predictions of cosmological models of galactic halo formation that inform us about the number and properties of streams around Milky Way-like galaxies. The insight gained from these comparisons will allow us to infer the properties of stream progenitors (masses, dynamics, metallicities, stellar populations). The changes in the host galaxies caused by the interactions with the dissolving companion galaxies will be another focus of our studies. We conclude by discussing synergies with WFIRST and Euclid, and also provide concrete suggestions for how the effects of scattered light could be minimized in LSST images to optimize the search for low surface brightness features, such as faint unresolved stellar tidal streams.

astro-ph.GA↗

arXiv2018

SMHASH: A new mid-infrared RR Lyrae distance determination for the Local Group dwarf spheroidal galaxy Sculptor

We present a new distance estimation for the Milky Way dwarf spheroidal satellite Sculptor obtained from multi-epoch mid-infrared observations of RR Lyrae stars. The 3.6 μm observations have been acquired with the Infrared Array Camera on board the Spitzer Space Telescope as part of the SMHASH Program. Mid-infrared light curves for 42 RRL were obtained, from which we measured Sculptor's distance modulus to be μ = 19.60 $\pm$ 0.02 (statistical) $\pm$ 0.04 (photometric) mag (with $σ_{sys}=$ = 0.09 mag), using the 3.6 μm empirical period-luminosity relations derived from the Galactic globular cluster M4, or μ = 19.57 $\pm$ 0.02 (statistical) $\pm$ 0.04 (photometric) mag (with $σ_{sys}=$ = 0.11 mag) using empirical relations in the same passband recently derived from the Large Magellanic Cloud globular cluster Reticulum. Both these measurements are in good agreement with values presented in previous works with Sculptor RR Lyrae stars in optical bands, and are also consistent with recent near-infrared RR Lyrae results. Best agreement with the literature is found for the latter modulus which is equivalent to a distance of d = 82 $\pm$ 1 (statistical) $\pm$ 2 (photometric) kpc (with $σ_{sys}=$ = 4 kpc). Finally, using a subsample of RR Lyrae stars with spectroscopic metallicities, we demonstrate that these distance estimates are not affected by metallicity effects.

astro-ph.GA↗

arXiv2017

SMHASH: Anatomy of the Orphan Stream using RR Lyrae stars

Stellar tidal streams provide an opportunity to study the motion and structure of the disrupting galaxy as well as the gravitational potential of its host. Streams around the Milky Way are especially promising as phase space positions of individual stars will be measured by ongoing or upcoming surveys. Nevertheless, it remains a challenge to accurately assess distances to stars farther than 10 kpc from the Sun, where we have the poorest knowledge of the Galaxy's mass distribution. To address this we present observations of 32 candidate RR Lyrae stars in the Orphan tidal stream taken as part of the Spitzer Merger History and Shape of the Galactic Halo (SMHASH) program. The extremely tight correlation between the periods, luminosities, and metallicities of RR Lyrae variable stars in the Spitzer IRAC $\mathrm{3.6 μm}$ band allows the determination of precise distances to individual stars; the median statistical distance uncertainty to each RR Lyrae star is $2.5\%$. By fitting orbits in an example potential we obtain an upper limit on the mass of the Milky Way interior to 60 kpc of $\mathrm{5.6_{-1.1}^{+1.2}\times 10^{11}\ M_\odot}$, bringing estimates based on the Orphan Stream in line with those using other tracers. The SMHASH data also resolve the stream in line--of--sight depth, allowing a new perspective on the internal structure of the disrupted dwarf galaxy. Comparing with N--body models we find that the progenitor had an initial dark halo mass of approximately $\mathrm{3.2 \times 10^{9}\ M_\odot}$, placing the Orphan Stream's progenitor amongst the classical dwarf spheroidals.

astro-ph.GA↗

arXiv2017

The Science Case for an Extended Spitzer Mission

Although the final observations of the Spitzer Warm Mission are currently scheduled for March 2019, it can continue operations through the end of the decade with no loss of photometric precision. As we will show, there is a strong science case for extending the current Warm Mission to December 2020. Spitzer has already made major impacts in the fields of exoplanets (including microlensing events), characterizing near Earth objects, enhancing our knowledge of nearby stars and brown dwarfs, understanding the properties and structure of our Milky Way galaxy, and deep wide-field extragalactic surveys to study galaxy birth and evolution. By extending Spitzer through 2020, it can continue to make ground-breaking discoveries in those fields, and provide crucial support to the NASA flagship missions JWST and WFIRST, as well as the upcoming TESS mission, and it will complement ground-based observations by LSST and the new large telescopes of the next decade. This scientific program addresses NASA's Science Mission Directive's objectives in astrophysics, which include discovering how the universe works, exploring how it began and evolved, and searching for life on planets around other stars.

astro-ph.EP↗

arXiv2017

At a Crossroads: Stellar Streams in the South Galactic Cap

We examine the distribution of old, metal-poor stars in a portion of the recently released PanSTARRs survey. We find an interesting confluence of four new cold stellar stream candidates that appear to converge on or pass near the south Galactic pole. The stream candidates, which we designate Murrumbidgee, Molonglo, Orinoco, and Kwando, lie at a distance of approximately 20 kpc and range in length from 13 to 95 degrees, or about 5 to 33 kpc. The stream candidates are between 100 and 300 pc in width, and are estimated to contain between 3000 and 8000 stars each, suggesting progenitors similar to modern day globular clusters. The trajectories of the streams imply orbits that range from hyperbolic to nearly circular. The Molonglo stream is nearly parallel to, at the same distance as, and offset by only 2.5 degrees from the previously discovered ATLAS stream, suggesting a possible common origin. Orinoco and Kwando also have similarly shaped, moderately eccentric, obliquely viewed orbits that suggest distinct progenitors within a common, larger parent body.

astro-ph.GA↗

arXiv2016

Tails from the Orphanage

Examining a portion of the northern Sloan Digital Sky Survey (SDSS) footprint, we detect at least three and possibly seven halo debris streams. One of these (PS1-D) was recently detected in the Pan-STARRS1 $3π$ survey, and the remaining two are also evident as extensions of the SDSS detections. All of these streams are metal poor and are found at a distance of around $21 \pm 5$ kpc. The streams are between 65\arcdeg~ and 70\arcdeg~ in length, oriented almost north-south, and are nearly parallel and somewhat convergent with the neighboring Orphan stream. Surface densities ranging from 1.5 to 0.5 stars per square degree down to $g = 21.7$ correspond to surface brightnesses between 35 and 37 mag per square arcsecond. The streams each appear to be more than 300 pc across, suggesting either dwarf/ultrafaint galaxy progenitors or long-term heating of very ancient globular cluster streams. The orbits of all but one of these streams appear to be nearly radial, and the orbit normals suggest that all of the streams are part of the Vast Polar Structure, a relatively narrow plane that contains most of the known satellite galaxies, globular clusters, and stellar streams.

astro-ph.GA↗

arXiv2016

Repeatability and Accuracy of Exoplanet Eclipse Depths Measured with Post-Cryogenic Spitzer

We examine the repeatability, reliability, and accuracy of differential exoplanet eclipse depth measurements made using the InfraRed Array Camera (IRAC) on the Spitzer Space Telescope during the post-cryogenic mission. We have re-analyzed an existing 4.5 μm data set, consisting of 10 observations of the XO-3b system during secondary eclipse, using seven different techniques for removing correlated noise. We find that, on average, for a given technique, the eclipse depth estimate is repeatable from epoch to epoch to within 156 parts per million (ppm). Most techniques derive eclipse depths that do not vary by more than a factor 3 of the photon noise limit. All methods but one accurately assess their own errors: for these methods, the individual measurement uncertainties are comparable to the scatter in eclipse depths over the 10 epoch sample. To assess the accuracy of the techniques as well as to clarify the difference between instrumental and other sources of measurement error, we have also analyzed a simulated data set of 10 visits to XO-3b, for which the eclipse depth is known. We find that three of the methods (BLISS mapping, Pixel Level Decorrelation, and Independent Component Analysis) obtain results that are within three times the photon limit of the true eclipse depth. When averaged over the 10 epoch ensemble, 5 out of 7 techniques come within 60 ppm of the true value. Spitzer exoplanet data, if obtained following current best practices and reduced using methods such as those described here, can measure repeatable and accurate single eclipse depths, with close to photon-limited results.

astro-ph.IM↗

arXiv2016

Metallicity and Age of the Stellar Stream Around the Disk Galaxy NGC 5907

Stellar streams have become central to studies of the interaction histories of nearby galaxies. To characterize the most prominent parts of the stellar stream around the well-known nearby (d = 17 Mpc) edge-on disk galaxy NGC 5907, we have obtained and analyzed new, deep gri Subaru/Suprime-Cam and 3.6 micron Spitzer/Infrared Array Camera (IRAC) observations. Combining the near-infrared 3.6 micron data with visible-light images allows us to use a long wavelength baseline to estimate the metallicity and age of the stellar population along a ~60 kpc long segment of the stream. We have fitted the stellar spectral energy distribution (SED) with a single-burst stellar population synthesis model and we use it to distinguish between the proposed satellite accretion and minor/major merger formation models of the stellar stream around this galaxy. We conclude that a massive minor merger (stellar mass ratio of at least 1:8) can best account for the metallicity of -0.3 inferred along the brightest parts of the stream.

astro-ph.GA↗