We undertake a new test of the metallicity sensitivity of the Leavitt Law for classical Cepheids. We derive an empirical calibration of the apparent luminosities of Cepheids as measured from the ...optical through the mid-infrared (0.45-8.0 Delta *mm) as a function of spectroscopic Fe/H abundances of individual Cepheids in the Large Magellanic Cloud (LMC) from Romaniello et al. The cumulative trend over the entire wavelength range shows a nearly monotonic behavior. The sense of the trend is consistent with differential line blanketing in the optical, leading to stars of high metallicity being fainter in the optical. This is followed by a reversal in the trend at longer wavelengths, with the crossover occurring near the K band at about 2.2 Delta *mm, consistent with a subsequent redistribution of energy resulting in a mild brightening of Cepheids (with increased metallicity) at mid-infrared wavelengths. This conclusion agrees with that of Romaniello et al. based on a differential comparison of the mean V- and K-band Leavitt Laws for the Galaxy, Small Magellanic Cloud, and LMC, but is opposite in sign to most other empirical tests of the sensitivity of Cepheid distances to mean O/H H II region abundances. We also search for a correlation of Cepheid host-galaxy metallicity with deviations of the galaxy's Cepheid distance from that predicted from a pure Hubble flow. Based on Cepheid distances to 26 nearby galaxies in the local flow, only a very weak signal is detected giving Delta *d Delta *m o = --0.17(? 0.31)(O/H -- 8.80) -- 0.21(? 0.10). This is in agreement with previous determinations, but statistically inconclusive.
The spatial distribution of oxygen in the interstellar medium of galaxies is the key to understanding how efficiently metals that are synthesized in massive stars can be redistributed across a ...galaxy. We present here a case study in the nearby spiral galaxy NGC 1365 using 3D optical data obtained in the TYPHOON Program. We find systematic azimuthal variations of the H ii region oxygen abundance imprinted on a negative radial gradient. The 0.2 dex azimuthal variations occur over a wide radial range of 0.3-0.7 R25 and peak at the two spiral arms in NGC 1365. We show that the azimuthal variations can be explained by two physical processes: gas undergoes localized, sub-kiloparsec-scale self-enrichment when orbiting in the inter-arm region, and experiences efficient, kiloparsec-scale mixing-induced dilution when spiral density waves pass through. We construct a simple chemical evolution model to quantitatively test this picture and find that our toy model can reproduce the observations. This result suggests that the observed abundance variations in NGC 1365 are a snapshot of the dynamical local enrichment of oxygen modulated by spiral-driven, periodic mixing and dilution.
Abstract
IC 1613 is an isolated dwarf galaxy within the Local Group. Low foreground and internal extinction, low metallicity, and low crowding make it an invaluable testbed for the calibration of the ...local distance ladder. We present new, high-fidelity distance estimates to IC 1613 via its Tip of the Red Giant Branch (TRGB) and its RR Lyrae (RRL) variables as part of the Carnegie-Chicago Hubble Program, which seeks an alternate local route to
H
0
using Population II stars. We have measured a TRGB magnitude
mag using wide-field observations obtained from the IMACS camera on the Magellan-Baade telescope. We have further constructed optical and near-infrared RRL light curves using archival
BI
- and new
H
-band observations from the ACS/WFC and WFC3/IR instruments on board the
Hubble Space Telescope
(
HST
). In advance of future
Gaia
data releases, we set provisional values for the TRGB luminosity via the Large Magellanic Cloud and Galactic RRL zero-points via
HST
parallaxes. We find corresponding true distance moduli
and
mag. We compare our results to a body of recent publications on IC 1613 and find no statistically significant difference between the distances derived from Population I and II stars.
Abstract
The Carnegie-Chicago Hubble Program (CCHP) is building a direct path to the Hubble constant (
H
0
) using Population II stars as the calibrator of the Type Ia supernova (SN Ia)-based ...distance scale. This path to calibrate the SNe Ia is independent of the systematics in the traditional Cepheid-based technique. In this paper, we present the distance to M101, the host to SN 2011fe, using the
I
-band tip of the red giant branch (TRGB) based on observations from the ACS/WFC instrument on the
Hubble Space Telescope
. The CCHP targets the halo of M101, where there is little to no host galaxy dust, the red giant branch is isolated from nearly all other stellar populations, and there is virtually no source confusion or crowding at the magnitude of the tip. Applying the standard procedure for the TRGB method from the other works in the CCHP series, we find a foreground-extinction-corrected M101 distance modulus of
μ
0
= 29.07 ± 0.04
stat
± 0.05
sys
mag, which corresponds to a distance of
D
= 6.52 ± 0.12
stat
± 0.15
sys
Mpc. This result is consistent with several recent Cepheid-based determinations, suggesting agreement between Population I and II distance scales for this nearby SN Ia host galaxy. We further analyze four archival data sets for M101 that have targeted its outer disk to argue that targeting in the stellar halo provides much more reliable distance measurements from the TRGB method owing to the combination of multiple structural components and heavy population contamination. Application of the TRGB in complex regions will have sources of uncertainty not accounted for in commonly used uncertainty measurement techniques.
ABSTRACT We provide evidence that UGC 1382, long believed to be a passive elliptical galaxy, is actually a giant low surface brightness (GLSB) galaxy that rivals the archetypical GLSB Malin 1 in ...size. Like other GLSB galaxies, it has two components: a high surface brightness disk galaxy surrounded by an extended low surface brightness (LSB) disk. For UGC 1382, the central component is a lenticular system with an effective radius of 6 kpc. Beyond this, the LSB disk has an effective radius of ∼38 kpc and an extrapolated central surface brightness of ∼26 mag arcsec−2. Both components have a combined stellar mass of ∼8 × 1010 M , and are embedded in a massive (1010 M ) low-density (<3 M pc−2) HI disk with a radius of 110 kpc, making this one of the largest isolated disk galaxies known. The system resides in a massive dark matter halo of at least 2 × 1012 M . Although possibly part of a small group, its low-density environment likely plays a role in the formation and retention of the giant LSB and HI disks. We model the spectral energy distributions and find that the LSB disk is likely older than the lenticular component. UGC 1382 has UV-optical colors typical of galaxies transitioning through the green valley. Within the LSB disk are spiral arms forming stars at extremely low efficiencies. The gas depletion timescale of ∼1011 years suggests that UGC 1382 may be a very-long-term resident of the green valley. We find that the formation and evolution of the LSB disk in UGC 1382 is best explained by the accretion of gas-rich LSB dwarf galaxies.
We introduce a new quantity, the mass flux density of galaxies evolving from the blue sequence to the red sequence. We propose a simple technique for constraining this mass flux using the ...volume-corrected number density in the extinction-corrected UV-optical color-magnitude distribution, the stellar age indexes H delta sub(A) and unk(4000), and a simple prescription for spectral evolution using a quenched star formation history. We exploit the excellent separation of red and blue sequences in the NUV - r band Hess function. The final value we measure, rho T = 0.033 m unk yr super(-1) Mpc super(-3), is strictly speaking an upper limit due to the possible contributions of bursting, composite, and extincted galaxies. However, it compares favorably with estimates of the average mass flux that we make based on the red luminosity function evolution derived from the DEEP2 and COMBO-17 surveys, rho R - +0034 M unk yr super(-1) Mpc super(-3). We find that the blue sequence mass has remained roughly constant since z = 1 ( rho B unk 0.01 M unk yr super(-1) Mpc super(-3), but the average on-going star formation of rho SF unk 0.037 M unk yr super(-1) Mpc super(-3) over 0 < z < 1 is balanced by mass flux off the blue sequence. We explore the nature of the galaxies in the transition zone with particular attention to the frequency and impact of active galactic nuclei (AGNs). The AGN fraction peaks in the transition zone. We find circumstantial, albeit weak evidence that the quench rates are higher in higher luminosity AGNs.
The local determination of the Hubble constant sits at a crossroad. Current estimates of the local expansion rate of the universe differ by about 1.7 , derived from the Cepheid- and TRGB-based ...calibrations, applied to Type Ia supernovae. To help elucidate possible sources of systematic error causing the tension, we show in this study the recently developed distance indicator, the J-region Asymptotic Giant Branch (JAGB) method, can serve as an independent cross-check and comparison with other local distance indicators. Furthermore, we make the case that the JAGB method has substantial potential as an independent, precise, and accurate calibrator of Type Ia supernovae for the determination of H0. Using the Local Group galaxy Wolf-Lundmark-Melotte (WLM), we present distance comparisons between the JAGB method, a TRGB measurement at near-infrared (JHK) wavelengths, a TRGB measurement in the optical I band, and a multiwavelength Cepheid period-luminosity relation determination. We find 0 ( JAGB ) = 24.97 0.02 ( stat ) 0.04 ( sys ) mag 0 ( TRGB NIR ) = 24.98 0.04 ( stat ) 0.07 ( sys ) mag 0 ( TRGB F 814 W ) = 24.93 0.02 ( stat ) 0.06 ( sys ) mag 0 ( Cepheids ) = 24.98 0.03 ( stat ) 0.04 ( sys ) mag . All four methods are in good agreement, confirming the local self-consistency of the four distance scales at the 3% level and adding confidence that the JAGB method is as accurate and as precise a distance indicator as either of the other three astrophysically based methods.
Abstract
The primary goal of the Carnegie Chicago Hubble Program (CCHP) is to calibrate the zero-point of the Type Ia supernova (SN Ia) Hubble Diagram through the use of Population II standard ...candles. So far, the CCHP has measured direct distances to 11 SNe Ia, and here we increase that number to 15 with two new Tip of the Red Giant Branch (TRGB) distances measured to NGC 5643 and NGC 1404. We present resolved, point-source photometry from new Hubble Space Telescope imaging of these two galaxies in the F814W and F606W bandpasses. From each galaxy’s stellar halo, we construct an F814W-band luminosity function in which we detect an unambiguous edge feature identified as the TRGB. For NGC 5643, we find
μ
0
= 30.48 ± 0.03(stat) ± 0.07(sys) mag, and for NGC 1404 we find
μ
0
= 31.36 ± 0.04(stat) ± 0.05(sys) mag. From a preliminary consideration of the SNe Ia in these galaxies, we find increased confidence in the results presented in Paper VIII. The high precision of our TRGB distances enables a significant measurement of the 3D displacement between the Fornax cluster galaxies NGC 1404 and NGC 1316 (Fornax A) equal to
1.50
−
0.39
+
0.25
Mpc, which we show is in agreement with independent constraints found in the literature.
We report deep Subaru H alpha observations of the extended ultraviolet (XUV) disk of M83. These new observations enable the first complete census of very young stellar clusters over the entire XUV ...disk. Combining Subaru and Galaxy Evolution Explorer data with a stellar population synthesis model, we find that (1) the standard, but stochastically sampled, initial mass function (IMF) is preferred over the truncated IMF because there are low-mass stellar clusters (10 super(2-3) M sub(middot in circle)) that host massive O-type stars; (2) the standard Salpeter IMF and a simple aging effect explain the counts of far-UV (FUV)-bright and H alpha -bright clusters with masses >10 super(3) M sub(middot in circle); and (3) the H alpha -to-FUV flux ratio over the XUV disk supports the standard IMF. To reach conclusion (2), we assumed instantaneous cluster formation and a constant cluster formation rate over the XUV disk. The Subaru Prime Focus Camera covers a large area even outside the XUV disk-far beyond the detection limit of the H I gas. This enables us to statistically separate the stellar clusters in the disk from background contamination. The new data, model, and previous spectroscopic studies provide overall consistent results with respect to the internal dust extinction (A sub(V) ~ 0.1 mag) and low metallicity (~0.2 Z sub(middot in circle)) using the dust extinction curve of the Small Magellanic Cloud. The minimum cluster mass for avoiding the upper IMF incompleteness due to stochastic sampling and the spectral energy distributions of O, B, and A stars are discussed in the Appendices.
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