Searcharxiv⌕ Search

arXiv subjects

Pieter van Dokkum

Publications and source records attributed to Pieter van Dokkum.

At least 163 records · Page 9Linked to original sources
arXiv2019

Spatially-resolved stellar kinematics of the ultra diffuse galaxy Dragonfly 44. I. Observations, kinematics, and cold dark matter halo fits

We present spatially-resolved stellar kinematics of the well-studied ultra diffuse galaxy (UDG) Dragonfly 44, as determined from 25.3 hrs of observations with the Keck Cosmic Web Imager. The luminosity-weighted dispersion within the half-light radius is $σ_{1/2}=33^{+3}_{-3}$ km/s. There is no evidence for rotation, with $V/σ<0.12$ (90% confidence) along the major axis, in apparent conflict with models where UDGs are the high-spin tail of the normal dwarf galaxy distribution. The spatially-averaged line profile is more peaked than a Gaussian, with Gauss-Hermite coefficient $h_4=0.13\pm 0.05$. The mass-to-light ratio within the effective radius is $M/L=26^{+7}_{-6}$, similar to other UDGs and higher by a factor of six than normal galaxies of the same luminosity. This difference between UDGs and other galaxies is, however, sensitive to the aperture that is used, and is much reduced when the $M/L$ ratios are measured within a fixed radius of 10 kpc. Dragonfly 44 has a rising velocity dispersion profile, from $σ=26^{+4}_{-4}$ km/s at R=0.2 kpc to $σ=41^{+8}_{-8}$ km/s at R=5.1 kpc. The profile can only be fit with a cuspy NFW profile if the orbital distribution has strong tangential anisotropy, with $β=-0.8^{+0.4}_{-0.5}$. An alternative explanation is that the dark matter profile has a core: a Di Cintio et al. (2014) density profile with a mass-dependent core provides a very good fit to the kinematics for a halo mass of $\log (M_{200}/{\rm M}_{\odot})=11.2^{+0.6}_{-0.6}$ and $β=-0.1^{+0.2}_{-0.3}$, i.e., isotropic orbits. This model predicts a slight positive kurtosis, in qualitative agreement with the measured $h_4$ parameter. UDGs such as Dragonfly 44 are dark matter dominated even in their centers, and can constrain the properties of dark matter in a regime where baryons usually dominate the kinematics: small spatial scales in massive halos.

astro-ph.GA↗
arXiv2019

Stellar Metallicities and Elemental Abundance Ratios of z~1.4 Massive Quiescent Galaxies

The chemical composition of galaxies has been measured out to z~4. However, nearly all studies beyond z~0.7 are based on strong-line emission from HII regions within star-forming galaxies. Measuring the chemical composition of distant quiescent galaxies is extremely challenging, as the required stellar absorption features are faint and shifted to near-infrared wavelengths. Here, we present ultra-deep rest-frame optical spectra of five massive quiescent galaxies at z~1.4, all of which show numerous stellar absorption lines. We derive the abundance ratios [Mg/Fe] and [Fe/H] for three out of five galaxies; the remaining two galaxies have too young luminosity-weighted ages to yield robust measurements. Similar to lower-redshift findings, [Mg/Fe] appears positively correlated with stellar mass, while [Fe/H] is approximately constant with mass. These results may imply that the stellar mass-metallicity relation was already in place at z~1.4. While the [Mg/Fe]-mass relation at z~1.4 is consistent with the z<0.7 relation, [Fe/H] at z~1.4 is ~0.2 dex lower than at z<0.7. With a [Mg/Fe] of 0.44(+0.08,-0.07) the most massive galaxy may be more alpha-enhanced than similar-mass galaxies at lower redshift, but the offset is less significant than the [Mg/Fe] of 0.6 previously found for a massive galaxy at z=2.1. Nonetheless, these results combined may suggest that [Mg/Fe] in the most massive galaxies decreases over time, possibly by accreting low-mass, less alpha-enhanced galaxies. A larger galaxy sample is needed to confirm this scenario. Finally, the abundance ratios indicate short star-formation timescales of 0.2-1.0 Gyr.

astro-ph.GA↗
arXiv2019

An Older, More Quiescent Universe from Panchromatic SED Fitting of the 3D-HST Survey

Galaxy observations are influenced by many physical parameters: stellar masses, star formation rates (SFRs), star formation histories (SFHs), metallicities, dust, black hole activity, and more. As a result, inferring accurate physical parameters requires high-dimensional models which capture or marginalize over this complexity. Here we re-assess inferences of galaxy stellar masses and SFRs using the 14-parameter physical model Prospector-$α$ built in the Prospector Bayesian inference framework. We fit the photometry of 58,461 galaxies from the 3D-HST catalogs at $0.5 < z < 2.5$. The resulting stellar masses are $\sim0.1-0.3$ dex larger than the fiducial masses while remaining consistent with dynamical constraints. This change is primarily due to the systematically older SFHs inferred with Prospector. The SFRs are $\sim0.1-1+$ dex lower than UV+IR SFRs, with the largest offsets caused by emission from "old" ($t>100$ Myr) stars. These new inferences lower the observed cosmic star formation rate density by $\sim0.2$ dex and increase the observed stellar mass growth by $\sim 0.1$ dex, finally bringing these two quantities into agreement and implying an older, more quiescent Universe than found by previous studies at these redshifts. We corroborate these results by showing that the Prospector-$α$ SFHs are both more physically realistic and are much better predictors of the evolution of the stellar mass function. Finally, we highlight examples of observational data which can break degeneracies in the current model; these observations can be incorporated into priors in future models to produce new & more accurate physical parameters.

astro-ph.GA↗
arXiv2019

Spatially Resolved Stellar Kinematics of the Ultra-Diffuse Galaxy Dragonfly 44: II. Constraints on Fuzzy Dark Matter

Given the absence of directly detected dark matter (DM) as weakly interacting massive particles, there is strong interest in the possibility that DM is an ultra-light scalar field, here denoted as fuzzy DM. Ultra-diffuse galaxies, with the sizes of giant galaxies and the luminosities of dwarf galaxies, have a wide range of DM halo masses, thus providing new opportunities for exploring the connections between galaxies and their DM halos. Following up on new integral field unit spectroscopic observations and dynamics modeling of the DM-dominated ultra-diffuse galaxy Dragonfly 44 in the outskirts of the Coma Cluster, we present models of fuzzy DM constrained by the stellar dynamics of this galaxy. We infer a scalar field mass of $\sim 3 \times 10^{-22}$ eV, consistent with other constraints from galaxy dynamics but in tension with constraints from Ly$α$ forest power spectrum modeling. While we are unable to statistically distinguish between fuzzy DM and normal cold DM models, we find that the inferred properties of the fuzzy DM halo satisfy a number of predictions for halos in a fuzzy DM cosmology. In particular, we find good agreement with the predicted core size--halo mass relation and the predicted transition radius between the quantum pressure-dominated inner region and the outer halo region.

astro-ph.GA↗
arXiv2019

On the Orbital Decay of Globular Clusters in NGC1052-DF2: Testing a Baryon-Only Mass Model

The dark matter content of the ultra diffuse galaxy NGC1052-DF2, as inferred from globular cluster (GC) and stellar kinematics, carries a considerable amount of uncertainty, with current constraints also allowing for the complete absence of dark matter. We test the viability of such a scenario by examining whether in a `baryon-only' mass model, the observed GC population experiences rapid orbital decay due to dynamical friction. Using a suite of 50 multi-GC N-body simulations that match observational constraints on both the stellar component of NGC1052-DF2 and its GC population but differ in the initial line-of-sight positions and the tangential velocities of the GCs, we show that there is a substantial amount of realization-to-realization variance in the evolution of the GCs. Nevertheless, over 10 Gyr, some of the GCs experience significant orbital evolution. Others evolve less. A combination of reduced dynamical friction in the galaxy core and GC-GC scattering keeps the GCs afloat, preventing them from sinking all the way to the galaxy center. While the current phase-space coordinates of the GCs are not unlikely for a baryon-only mass model, the GC system does evolve over time. Therefore, if NGC1052-DF2 has no dark matter, some of its GCs must have formed further out, and the GC system must have been somewhat more extended in the past. The presence of a low mass cuspy halo, while allowed by the kinematics, seems improbable as significantly shorter inspiral timescales in the central region would quickly lead to the formation of a nuclear star cluster.

astro-ph.GA↗
arXiv2019

On the detectability of visible-wavelength line emission from the local circumgalactic and intergalactic medium

We describe a new approach to studying the intergalactic and circumgalactic medium in the local Universe: direct detection through narrow-band imaging of ultra-low surface brightness visible-wavelength line emission. We use the hydrodynamical cosmological simulation EAGLE to investigate the expected brightness of this emission at low redshift ($z$ $\lesssim$ 0.2). H$α$ emission in extended halos (analogous to the extended Ly$α$ halos/blobs detected around galaxies at high redshifts) has a surface brightness of $\gtrsim700$ photons cm$^{-2}$ sr$^{-1}$ s$^{-1}$ out to $\sim$100 kpc. Mock observations show that the Dragonfly Telephoto Array, equipped with state-of-the-art narrow-band filters, could directly image these structures in exposure times of $\sim$10 hours. H$α$ fluorescence emission from this gas can be used to place strong constraints on the local ultra-violet background, and on gas flows around galaxies. Detecting H$α$ emission from the diffuse intergalactic medium (the "cosmic web") is beyond current capabilities, but would be possible with a hypothetical 1000-lens Dragonfly array.

astro-ph.GA↗
arXiv2019

Measuring Star-Formation Histories, Distances, and Metallicities with Pixel Color-Magnitude Diagrams I: Model Definition and Mock Tests

We present a comprehensive study of the applications of the pixel color-magnitude diagram (pCMD) technique for measuring star formation histories (SFHs) and other stellar population parameters of galaxies, and demonstrate that the technique can also constrain distances. SFHs have previously been measured through either the modeling of resolved-star CMDs or of integrated-light SEDs, yet neither approach can easily be applied to galaxies in the "semi-resolved regime". The pCMD technique has previously been shown to have the potential to measure stellar populations and star formation histories in semi-resolved galaxies. Here we present Pixel Color-Magnitude Diagrams with Python (pcmdpy), a GPU-accelerated package that makes significant computational improvements to the original code and including more realistic physical models. These advances include the simultaneous fitting of distance, modeling a Gaussian metallicity-distribution function, and an observationally-motivated dust model. GPU-acceleration allows these more realistic models to be fit roughly 7x faster than the simpler models in the original code. We present results from a suite of mock tests, showing that with proper model assumptions, the code can simultaneously recover SFH, [Fe/H], distance, and dust extinction. Our results suggest the code, applied to observations with HST-like resolution, should constrain these properties with high precision within 10 Mpc and can be applied to systems out to as far as 100 Mpc. pCMDs open a new window to studying the stellar populations of many galaxies that cannot be readily studied through other means.

astro-ph.GA↗
arXiv2019

A second galaxy missing dark matter in the NGC1052 group

The ultra-diffuse galaxy NGC1052-DF2 has a very low velocity dispersion, indicating that it has little or no dark matter. Here we report the discovery of a second galaxy in this class, residing in the same group. NGC1052-DF4 closely resembles NGC1052-DF2 in terms of its size, surface brightness, and morphology; has a similar distance of $D=19.9\pm 2.8$ Mpc; and also has a population of luminous globular clusters extending out to 7 kpc from the center of the galaxy. Accurate radial velocities of the diffuse galaxy light and seven of the globular clusters were obtained with the Low Resolution Imaging Spectrograph on the Keck I telescope. The velocity of the diffuse light is identical to the median velocity of the clusters, $v_{\rm sys}=\langle v_{\rm gc} \rangle=1445$ km/s, and close to the central velocity of the NGC1052 group. The rms spread of the observed velocities is very small at $σ_{\rm obs}=5.8$ km/s. Taking observational uncertainties into account we determine an intrinsic velocity dispersion of $σ_{\rm intr}=4.2^{+4.4}_{-2.2}$ km/s, consistent with the expected value from the stars alone ($σ_{\rm stars}\approx 7$ km/s) and lower than expected from a standard NFW halo ($σ_{\rm halo}\sim 30$ km/s). We conclude that NGC1052-DF2 is not an isolated case but that a class of such objects exists. The origin of these large, faint galaxies with an excess of luminous globular clusters and an apparent lack of dark matter is, at present, not understood.

astro-ph.GA↗
arXiv2019

Still Missing Dark Matter: KCWI High-Resolution Stellar Kinematics of NGC1052-DF2

The velocity dispersion of the ultra diffuse galaxy NGC1052-DF2 was found to be $σ_{\rm gc}=7.8^{+5.2}_{-2.2} \ \mathrm{kms^{-1}}$, much lower than expected from the stellar mass -- halo mass relation and nearly identical to the expected value from the stellar mass alone. This result was based on the radial velocities of ten luminous globular clusters that were assumed to be associated with the galaxy. A more precise measurement is possible from high resolution spectroscopy of the diffuse stellar light. Here we present an integrated spectrum of the diffuse light of NGC1052-DF2 obtained with the Keck Cosmic Web Imager, with an instrumental resolution of $σ_{\rm instr}\approx 12 \ \mathrm{kms^{-1}}$. The systemic velocity of the galaxy is $v_{\rm sys}=1805\pm 1.1 \ \mathrm{kms^{-1}}$, in very good agreement with the average velocity of the globular clusters ($\langle v_{\rm gc}\rangle = 1803\pm 2 \ \mathrm{kms^{-1}}$). There is no evidence for rotation within the KCWI field of view. We find a stellar velocity dispersion of $σ_{\rm stars}=8.4 \pm 2.1 \ \mathrm{kms^{-1}}$, consistent with the dispersion that was derived from the globular clusters. The implied dynamical mass within the half-light radius $r_{1/2}=2.7 \ \mathrm{kpc}$ is $M_{\rm dyn}= (1.3 \pm 0.8) \times 10^8 $ M$_{\odot}$, similar to the stellar mass within that radius ($M_{\rm stars}=(1.0 \pm 0.2) \times 10^8 \ \mathrm{M}_{\odot}$). With this confirmation of the low velocity dispersion of NGC1052-DF2, the most urgent question is whether this "missing dark matter problem" is unique to this galaxy or applies more widely.

astro-ph.GA↗
arXiv2019

Galaxy Merger Fractions in Two Clusters at $z\sim2$ Using the Hubble Space Telescope

We measure the fraction of galaxy-galaxy mergers in two clusters at $z\sim2$ using imaging and grism observations from the {\it Hubble Space Telescope}. The two galaxy cluster candidates were originally identified as overdensities of objects using deep mid-infrared imaging and observations from the {\it Spitzer Space Telescope}, and were subsequently followed up with HST/WFC3 imaging and grism observations. We identify galaxy-galaxy merger candidates using high resolution imaging with the WFC3 in the F105W, F125W, and F160W bands. Coarse redshifts for the same objects are obtained with grism observations in G102 for the $z\sim1.6$ cluster (IRC0222A) and G141 for the $z\sim2$ cluster (IRC0222B). Using visual classifications as well as a variety of selection techniques, we measure merger fractions of $11_{-3.2}^{+8.2}$ in IRC0222A and $18_{-4.5}^{+7.8}$ in IRC0222B. In comparison, we measure a merger fraction of $5.0_{-0.8}^{+1.1}\%$ for field galaxies at $z\sim2$. Our study indicates that the galaxy-galaxy merger fraction in clusters at $z\sim2$ is enhanced compared the field population, but note that more cluster measurements at this epoch are needed to confirm our findings.

astro-ph.GA↗
arXiv2019

The distance to NGC1042 in the context of its proposed association with the dark matter-deficient galaxies NGC1052-DF2 and NGC1052-DF4

It has been suggested that the dark matter-deficient galaxies NGC1052-DF2 and NGC1052-DF4 might not be members of the NGC1052 group but in the foreground at $\sim 13$ Mpc, and satellites of the bright spiral galaxy NGC1042. We previously showed that the CMDs of the galaxies are inconsistent with this hypothesis, and derived distances of 19-20 Mpc from their surface brightness fluctuation signals. Here we note that NGC1042 is almost certainly a member of the NGC1052 group as well, based on its radial velocity, the HI distribution in the NGC1052/NGC1042 system, and the Tully-Fisher relation.

astro-ph.GA↗
arXiv2019

A New View of the Size-Mass Distribution of Galaxies: Using $r_{20}$ and $r_{80}$ instead of $r_{50}$

When investigating the sizes of galaxies it is standard practice to use the half-light radius, $r_{50}$. Here we explore the effects of the size definition on the distribution of galaxies in the size -- stellar mass plane. Specifically, we consider $r_{20}$ and $r_{80}$, the radii that contain 20% and 80% of a galaxy's total luminosity, as determined from a Sersic profile fit, for galaxies in the 3D-HST/CANDELS and COSMOS-DASH surveys. These radii are calculated from size catalogs based on a simple calculation assuming a Sersic profile. We find that the size-mass distributions for $r_{20}$ and $r_{80}$ are markedly different from each other and also from the canonical $r_{50}$ distribution. The most striking difference is in the relative sizes of star forming and quiescent galaxies at fixed stellar mass. Whereas quiescent galaxies are smaller than star forming galaxies in $r_{50}$, this difference nearly vanishes for $r_{80}$. By contrast, the distance between the two populations increases for $r_{20}$. Considering all galaxies in a given stellar mass and redshift bin we detect a significant bimodality in the distribution of $r_{20}$, with one peak corresponding to star forming galaxies and the other to quiescent galaxies. We suggest that different measures of the size are tracing different physical processes within galaxies; $r_{20}$ is closely related to processes controlling the star formation rate of galaxies and $r_{80}$ may be sensitive to accretion processes and the relation of galaxies with their halos.

astro-ph.GA↗
arXiv2019

High Redshift Massive Quiescent Galaxies are as Flat as Star Forming Galaxies: The Flattening of Galaxies and the Correlation with Structural Properties in CANDELS/3D-HST

We investigate the median flattening of galaxies at $0.2 10^{11}M_{\odot}$ are rounder than those at lower masses, consistent with the hypothesis that they have grown significantly through dry merging. The massive quiescent galaxies at higher redshift become flatter, and are as flat as star forming massive galaxies at $2.5<z<3.5$, consistent with formation through direct transformations or wet mergers. We find that in quiescent galaxies, correlations with $q_{med}$ and $M_{*}$, $z$ and $r_{e}$ are driven by the evolution in the sérsic index ($n$), consistent with the growing accumulation of minor mergers at lower redshift. Interestingly, $n$ does not drive these trends fully in star-forming galaxies. Instead, the strongest predictor of $q$ in star-forming galaxies is the effective radius, where larger galaxies are flatter. Our findings suggest that $q_{med}$ is tracing bulge-to-total ($B/T$) galaxy ratio which would explain why smaller/more massive star-forming galaxies are rounder than their extended/less massive analogues, although it is unclear why sérsic index correlates more weakly with flattening for star forming galaxies than for quiescent galaxies.

astro-ph.GA↗
arXiv2018

HST/WFC3 grism observations of $z~\mathtt{\sim}~1$ clusters: The cluster vs. field stellar mass-size relation and evidence for size growth of quiescent galaxies from minor mergers

Minor mergers are thought to be responsible for the size growth of quiescent field galaxies with decreasing redshift. We test this hypothesis using the cluster environment as a laboratory. Satellite galaxies in clusters move at high velocities, making mergers between them rare. The stellar mass-size relation in ten clusters and in the field is measured and compared at $z~\mathtt{\sim}~1$. Our cluster sample contains 344 spectroscopically-confirmed cluster members with Gemini/GMOS and 182 confirmed with HST WFC3 G141 grism spectroscopy. On average, quiescent and star-forming cluster galaxies are smaller than their field counterparts by ($0.08\pm0.04$) dex and ($0.07\pm0.01$) dex respectively. These size offsets are consistent with the average sizes of quiescent and star-forming field galaxies between $1.2\leqslant z\leqslant1.5$, implying the cluster environment has inhibited size growth between this period and $z~\mathtt{\sim}~1$. The negligible differences measured between the $z~\mathtt{\sim}~0$ field and cluster quiescent mass-size relations in other works imply that the average size of quiescent cluster galaxies must rise with decreasing redshift. Using a toy model, we show that the disappearance of the compact cluster galaxies might be explained if, on average, $\mathtt{\sim}40\%$ of them merge with their brightest cluster galaxies (BCGs) and $\mathtt{\sim}60\%$ are tidally destroyed into the intra-cluster light (ICL) between $0\leqslant z\leqslant1$. This is in agreement with the observed stellar mass growth of BCGs between $0\leqslant z\leqslant1$ and the observed ICL stellar mass fraction at $z~\mathtt{\sim}~0$. Our results support minor mergers as the cause for the size growth in quiescent field galaxies, with cluster-specific processes responsible for the similarity between the field and cluster quiescent mass-size relations at low redshift.

astro-ph.GA↗
arXiv2018

Revisiting the Size-Luminosity Relation in the Era of Ultra Diffuse Galaxies

Galaxies are generally found to follow a relation between their size and luminosity, such that luminous galaxies typically have large sizes. The recent identification of a significant population of galaxies with large sizes but low luminosities ("ultra diffuse galaxies", or UDGs) raises the question whether the inverse is also true, that is, whether large galaxies typically have high luminosities. Here we address this question by studying a size-limited sample of galaxies in the Coma cluster. We select red cluster galaxies with sizes $r_{\mathrm{eff}} > 2 \ \mathrm{kpc}$ down to $M_{g} \sim -13 \ \mathrm{mag}$ in an area of $9 \ \mathrm{deg}^2$, using carefully-filtered CFHT images. The sample is complete to a central surface brightness of $μ_{g,0}\approx 25.0 \ \mathrm{mag\,arcsec}^{-2}$ and includes 90% of Dragonfly-discovered UDGs brighter than this limit. Unexpectedly, we find that red, large galaxies have a fairly uniform distribution in the size-luminosity plane: there is no peak at the absolute magnitude implied by the canonical size-luminosity relation. The number of galaxies within $\pm 0.5$ magnitudes of the canonical peak ($M_g = -19.69$ for $2<r_{\mathrm{eff}}<3$ kpc) is a factor of $\sim 9$ smaller than the number of fainter galaxies with $-19<M_g<-13$. Large, faint galaxies such as UDGs are far more common than large galaxies that are on the size-luminosity relation. An implication is that, for large galaxies, size is not an indicator of halo mass. Finally, we show that the structure of faint large galaxies is different from that of bright large galaxies: at fixed large size, the Sérsic index decreases with magnitude following the relation $\log_{10} n \approx -0.067M_g-0.989$.

astro-ph.GA↗
arXiv2018

Spectroscopic Constraints on the Build-up of the Intracluster Light in the Coma Cluster

The stellar content of the intracluster light (ICL) provides unique insight into the hierarchical assembly process of galaxy clusters.However, the ICL is difficult to study due to its low surface brightness and large physical extent. We present optical spectra of three ICL regions in the Coma cluster, located between 100-180kpc from their nearest BCGs: NGC4889 and NGC4874. The mean surface brightness of the three ICL regions are μ$_g$~25.3-26.2mag arcsec$^{-2}$. IFU spectroscopy with 13.5 hr on-source integration time were acquired as part of an ancillary program within the SDSS-IV MaNGA survey. We stacked the 127 individual fiber spectra in each IFU in order to achieve a 1σ limiting surface brightness of 27.9mag arcsec$^{-2}$, corresponding to a mean S/N in the optical of 21.6,9.6,and 11.6Å$^{-1}$. We apply stellar population models to the stacked spectra, and measure the recession velocities, velocity dispersions ($σ$), stellar ages, and [Fe/H]. Our results show that the $σ$ of ICL regions are very high, indicating the stars are tracing the gravitational potential of the cluster, instead of any individual galaxy. The line-of-sight velocities of the three ICL regions are different from each other by ~700km/s, while the velocity of each region is similar to the closest BCG. This suggests that the ICL regions are associated with two distinct subclusters centered on NGC4889 and NGC4874.The stellar populations of these regions are old and metal poor, with ages of 7-12Gyr, and [Fe/H] of -0.8 to -0.6 dex. From the derived age and [Fe/H], the build-up of ICL in Coma is likely to be through the accretion of low mass galaxies or the tidal stripping of the outskirts of massive galaxies that have ended their star formation early on, instead of directly from major mergers of massive galaxies.

astro-ph.GA↗
arXiv2018

Complete IRAC mapping of the CFHTLS-DEEP, MUSYC AND NMBS-II FIELDS

The IRAC mapping of the NMBS-II fields program is an imaging survey at 3.6 and 4.5$μ$m with the Spitzer Infrared Array Camera (IRAC). The observations cover three Canada-France-Hawaii Telescope Legacy Survey Deep (CFHTLS-D) fields, including one also imaged by AEGIS, and two MUSYC fields. These are then combined with archival data from all previous programs into deep mosaics. The resulting imaging covers a combined area of about 3 $deg^2$, with at least $\sim$2 hr integration time for each field. In this work, we present our data reduction techniques and document the resulting coverage maps at 3.6 and 4.5$μ$m. All of the images are W-registered to the reference image, which is either the z-band stack image of the 25\% best seeing images from the CFHTLS-D for CFHTLS-D1, CFHTLS-D3, and CFHTLS-D4, or the K-band images obtained at the Blanco 4-m telescope at CTIO for MUSYC1030 and MUSYC1255. We make all images and coverage maps described herein publicly available via the Spitzer Science Center.

astro-ph.GA↗
arXiv2018

The Distance of the Dark Matter Deficient Galaxy NGC1052-DF2

We recently inferred that the galaxy NGC1052-DF2 has little or no dark matter and a rich system of unusual globular clusters. We assumed that the galaxy is a satellite of the luminous elliptical galaxy NGC1052 at ~20 Mpc, on the basis of its surface brightness fluctuations (SBF) distance of $19.0 \pm 1.7$ Mpc, its radial velocity of ~1800 km/s, and its projected position. Here we analyze the color-magnitude diagram (CMD) of NGC1052-DF2, following the suggestion by Trujillo et al. (2018) that the tip of the red giant branch (TRGB) can be detected in currently available HST data and the galaxy is at ~13 Mpc. Using fully populated galaxy models we show that the CMD is strongly influenced by blends. These blends produce a "phantom" TRGB ~2 times brighter than the true TRGB, which can lead to erroneous distance estimates ~1.4 times smaller than the actual distance. We compare NGC1052-DF2 to model images as well as other galaxies in our HST sample, and show that the large population of unblended RGB stars expected for distances of ~13 Mpc is not detected. We also provide a new distance measurement to NGC1052-DF2 that is free of calibration uncertainties, by anchoring it to a satellite of the megamaser host galaxy NGC4258. From a megamaser-TRGB-SBF distance ladder we obtain $D=18.7 \pm 1.7$ Mpc, consistent with our previous measurement and with the distance to the elliptical galaxy NGC1052.

astro-ph.GA↗