arXiv subjects

Garth D. Illingworth

Publications and source records attributed to Garth D. Illingworth.

At least 91 records · Page 5Linked to original sources

arXiv2004

From z>6 to z~2: Unearthing Galaxies at the Edge of the Dark Ages

Galaxies undergoing formation and evolution can now be observed over a time baseline of some 12 Gyr. An inherent difficulty with high-redshift observations is that the objects are very faint and the best resolution (HST) is only ~0.5 kpc. Such studies thereby combine in a highly synergistic way with the great detail that can be obtained for nearby galaxies. 3 new developments are highlighted. First is the derivation of stellar masses for galaxies from SEDs using HST and now Spitzer data, and dynamical masses from both sub-mm observations of CO lines and near-IR observations of optical lines like Halpha. A major step has been taken with evidence that points to the z~2-3 LBGs having masses that are a few x 10^10 Msolar. Second is the discovery of a population of evolved red galaxies at z~2-3 which appear to be the progenitors of the more massive early-type galaxies of today, with dynamical masses around a few x 10^11 Msolar. Third are the remarkable advances that have occurred in characterizing dropout galaxies to z~6 and beyond, < 1 Gyr from recombination. The HST ACS has played a key role here, with the dropout technique being applied to i & z images in several deep ACS fields, yielding large samples of these objects. This has allowed a detailed determination of their properties and meaningful comparisons against lower-z samples. The use of cloning techniques has overcome many of the strong selection biases affecting the study of these objects. A clear trend of size with redshift has been identified, and its impact on the luminosity density and SFR estimated. There is a significant though modest decrease in the SFR from z~2.5 to z~6. The latest data also allow for the first robust determination of the LF at z~6. Finally, the latest UDF ACS and NICMOS data has resulted in the detection of some galaxies at z~7-8.

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arXiv2004

Infall, the Butcher-Oemler Effect, and the Descendants of Blue Cluster Galaxies at z~0.6

Using wide-field HST/WFPC2 imaging and extensive Keck/LRIS spectroscopy, we present a detailed study of the galaxy populations in MS2053--04, a massive, X-ray luminous cluster at z=0.5866. Analysis of 149 confirmed cluster members shows that MS2053 is composed of two structures that are gravitationally bound to each other; their respective velocity dispersions are 865 km/s (113 members) and 282 km/s (36 members). MS2053's total dynamical mass is 1.2x10^15 Msun. MS2053 is a classic Butcher-Oemler cluster with a high fraction of blue members (24%) and an even higher fraction of star-forming members (44%), as determined from their [OII] emission. The number fraction of blue/star-forming galaxies is much higher in the infalling structure than in the main cluster. This result is the most direct evidence to date that the Butcher-Oemler effect is linked to galaxy infall. In terms of their colors, luminosities, estimated internal velocity dispersions, and [OII] equivalent widths, the infalling galaxies are indistinguishable from the field population. MS2053's deficit of S0 galaxies combined with its overabundance of blue spirals implies that many of these late-types will evolve into S0 members. The properties of the blue cluster members in both the main cluster and infalling structure indicate they will evolve into low mass, L 3.

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arXiv2004

Galaxies at z~7-8: z-dropouts in the Hubble Ultra Deep Field

We have detected likely z~7-8 galaxies in the 144"x144" NICMOS observations of the Hubble Ultra Deep Field. Objects are required to be >3 sigma detections in both NICMOS bands, J and H. The selection criteria for this sample are (z-J)>0.8, (z-J) > 0.66 (J-H)+0.8, (J-H)<1.2, and no detection at <8500 Angstroms. The 5 selected sources have total magnitudes H~27. Four of the five sources are quite blue compared to typical lower-redshift dropout galaxies and are clustered within a 1 arcmin**2 region. Because all 5 sources are near the limit of the NICMOS data, we have carefully evaluated their reality. Each of the candidates is visible in different splits of the data and a median stack. We analyzed several noise images and estimate the number of spurious sources to be 1+/-1. A search using an independent reduction of this same data set clearly revealed 3 of the 5 candidates and weakly detected a 4th candidate, suggesting the contamination could be higher. For comparison with predictions from lower redshift samples we take a conservative approach and adopt four z~7-8 galaxies as our sample. With the same detection criteria on simulated datasets, assuming no-evolution from z~3.8, we predict 10 sources at z~7-8, or 14 if we use a more realistic (1+z)^{-1} size scaling. We estimate that the rest-frame continuum UV (~1800 Angstroms) luminosity density at z~7.5 (integrated down to 0.3L*) is just 0.20_{-0.08}^{+0.12}x that found at z~3.8. Effectively this sets an upper limit on the luminosity density down to 0.3 L*. This result is consistent with significant evolution at the bright end of the luminosity function from z~7.5 to z~3.8. Even with the lower UV luminosity density at z~7.5, it appears that galaxies could still play an important role in reionization at these redshifts, though definitive measurements remain to be made. [abridged]

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arXiv2004

Field E+A Galaxies at Intermediate Redshifts (0.3<z<1)

We select E+A candidates from a spectroscopic dataset of ~800 field galaxies and measure the E+A fraction at 0.3<z<1 to be 2.7+/-1.1%, a value lower than that in galaxy clusters at comparable redshifts (11+/-3%). HST/WFPC2 imaging for five of our six E+A's shows they have a heterogeneous parent population: these E+A's span a range in half-light radius (0.8-8 kpc) and estimated internal velocity dispersion (50-220 km/s), and they include luminous systems (-21.6<M_Bz-5logh<-19.2). Despite their diversity in some aspects, the E+A's share several common characteristics that indicate the E+A phase is an important link in the evolution of star-forming galaxies into passive systems: the E+A's are uniformly redder than the blue, star-forming galaxies that make up the majority of the field, they are more likely to be bulge-dominated than the average field galaxy, and they tend to be morphologically irregular. We find E+A's make up ~9% of the absorption line systems in this redshift range, and estimate that ~25% of passive galaxies in the local field had an E+A phase at z<1.

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arXiv2003

The detailed Fundamental Plane of two high redshift clusters: MS 2053-04 at z=0.58 and MS 1054-03 at z=0.83

We study the fundamental plane relation in high redshift clusters using a sample of 26 galaxies in MS 2053-04 (z=0.583) and 22 galaxies in MS 1054-03 (z=0.83). The zeropoint and scatter are compared to results for lower redshift clusters in order to trace evolutionary effects. Furthermore, our large sample enables us to investigate correlations between residuals from the fundamental plane and other characteristics of the galaxies, such as color, $Hβ$ linestrength, spatial distribution, and mass. The observed scatter of the early-type galaxies with sigma > 100 km/s around the fundamental plane is 0.134 and 0.106 in log r_e for MS 2053-04 and MS 1054-03 respectively. The residuals from the fundamental plane of MS 2053-04 are correlated with residuals from the $Hβ- σ$ relation, suggesting that stellar populations are playing a role in shaping the fundamental plane. The measured evolution in log M/L is influenced by selection effects, as galaxies with lower M/L in the Johnson B-band enter a magnitude-limited sample more easily. When we select high mass early-type galaxies to avoid this bias, we find $\log M/L_B \sim -0.47 z$ and a formation redshift $z_{form} \sim 2.95$, similar to earlier results.

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arXiv2003

The DEEP Groth Strip Survey IX: Evolution of the Fundamental Plane of Field Galaxies

Fundamental Plane studies provide an excellent means of understanding the evolutionary history of early-type galaxies. Using the Low Resolution Imaging Spectrograph on the Keck telescope, we obtained internal stellar kinematic information for 36 field galaxies in the Groth Strip--21 early-type and 15 disk galaxies. Their redshifts range from 0.3--1.0, with a median redshift 0.8. The slope of the relation shows no difference compared with the local slope. However, there is significant evolution in the zero-point offset; an offset due to evolution in magnitude requires a 2.4 magnitude luminosity brightening at z=1. We see little differences of the offset with bulge fraction, which is a good surrogate for galaxy type. Correcting for the luminosity evolution reduces the orthogonal scatter in the Fundamental Plane to 8%, consistent with the local scatter. This scatter is measured for our sample, and does not include results from other studies which may have different selection effects. The difference in the degree of evolution between our field sample and published cluster galaxies suggests a more recent formation epoch--around z=1.5 for field galaxies compared to z>2.0 for cluster galaxies. The magnitude difference implies that the field early-type galaxies are about 2 Gyr younger than the cluster ellipticals using standard single-burst models. However, the same models imply a significant change in the rest-frame U-B color from then to present, which is not seen in our sample. Continuous low-level star formation, however, would serve to explain the constant colors over this large magnitude change. A consistent model has 7% of the stellar mass created after the initial burst, using an exponentially decaying star formation rate with an e-folding time of 5 Gyr.

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arXiv2003

Spectroscopic Confirmation of a Substantial Population of Luminous Red Galaxies at Redshifts z>2

We confirm spectroscopically the existence of a population of galaxies at z>~2 with rest-frame optical colors similar to normal nearby galaxies. The galaxies were identified by their red near-infrared colors in deep images obtained with ISAAC on the Very Large Telescope. Redshifts of six galaxies with Js-Ks>2.3 were measured from optical spectra obtained with the Keck Telescope. Five out of six are in the range 2.43<=z<=3.52, demonstrating that the Js-Ks color selection is quite efficient. The rest-frame ultraviolet spectra of confirmed z>2 galaxies display a range of properties, with two galaxies showing emission lines characteristic of AGN, two having Ly-alpha in emission, and one showing interstellar absorption lines only. Their full spectral energy distributions are well described by constant star formation models with ages 1.4-2.6 Gyr, except for one galaxy whose colors indicate a dusty starburst. The confirmed z>2 galaxies are very luminous, with Ks=19.2-19.9. Assuming that our bright spectroscopic sample is representative for the general population of Js-Ks selected objects, we find that the surface density of red z>~2 galaxies is ~0.9/arcmin^2 to Ks=21. The surface density is comparable to that of Lyman-break selected galaxies with Ks<21, when corrections are made for the different redshift distributions of the two samples. Although there will be some overlap between the two populations, most 'optical-break' galaxies are too faint in the rest-frame ultraviolet to be selected as Lyman-break galaxies. The most straightforward interpretation is that star formation in typical optical-break galaxies started earlier than in typical Lyman-break galaxies. Optical-break galaxies may be the oldest and most massive galaxies yet identified at z>2, and could evolve into early-type galaxies and bulges.

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arXiv2003

Discovery of Two Distant Type Ia Supernovae in the Hubble Deep Field North with the Advanced Camera for Surveys

We present observations of the first two supernovae discovered with the recently installed Advanced Camera for Surveys (ACS) on the Hubble Space Telescope. The supernovae were found in Wide Field Camera images of the Hubble Deep Field North taken with the F775W, F850LP, and G800L optical elements as part of the ACS guaranteed time observation program. Spectra extracted from the ACS G800L grism exposures confirm that the objects are Type Ia supernovae (SNe Ia) at redshifts z=0.47 and z=0.95. Follow-up HST observations have been conducted with ACS in F775W and F850LP and with NICMOS in the near-infrared F110W bandpass, yielding a total of 9 flux measurements in the 3 bandpasses over a period of 50 days in the observed frame. We discuss many of the important issues in doing accurate photometry with the ACS. We analyze the multi-band light curves using two different fitting methods to calibrate the supernovae luminosities and place them on the SNe Ia Hubble diagram. The resulting distances are consistent with the redshift-distance relation of the accelerating universe model, although evolving intergalactic grey dust remains as a less likely possibility. The relative ease with which these SNe Ia were found, confirmed, and monitored demonstrates the potential ACS holds for revolutionizing the field of high-redshift SNe Ia, and therefore of testing the accelerating universe cosmology and constraining the "epoch of deceleration".

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arXiv2002

The DEEP Groth Strip Survey II. Hubble Space Telescope Structural Parameters of Galaxies in the Groth Strip

The quantitative morphological classification of distant galaxies is essential to the understanding of the evolution of galaxies over the history of the Universe. This paper presents Hubble Space Telescope WFPC2 F606W and F814W photometric structural parameters for 7450 galaxies in the ``Groth Strip.'' These parameters are based on a two-dimensional bulge+disk surface brightness model and were obtained using an automated reduction and analysis pipeline described in detail here. A first set of fits was performed separately in each bandpass, and a second set of fits was performed simultaneously on both bandpasses. The information produced by these two types of fits can be used to explore different science goals. Systematic and random fitting errors in all structural parameters as well as bulge and disk colors are carefully characterized through extensive sets of simulations. The results of these simulations are given in catalogs similar to the real science catalogs so that both real and simulated measurements can be sampled according to the same selection criteria to show biases and errors in the science data subset of interest. The effects of asymmetric structures on the recovered bulge+disk fitting parameters are also explored through simulations. The full multidimensional photometric survey selection function of the Groth Strip is also computed. This selection function, coupled to bias maps from simulations, provides a complete and objective reproduction of the observational limits, and these limits can be applied to theoretical predictions from galaxy evolution models for direct comparisons with the data.

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arXiv2001

Luminosity Evolution of Field Early-Type Galaxies to z=0.55

We study the Fundamental Plane of field early-type galaxies at intermediate redshift, using HST WFPC2 observations and deep Keck spectroscopy. Structural parameters and internal velocity dispersions are measured for eighteen galaxies at 0.15 < z < 0.55. Rest frame M/L_B ratios are determined from the Fundamental Plane and compared to those of cluster early-type galaxies at the same redshifts. The systematic offset between M/L ratios of field and cluster early-type galaxies at intermediate redshift is small, and not significant: (field) - (cluster) = -0.18 +- 0.11. The M/L ratios of field early-type galaxies evolve as Δ(ln M/L_B) = (-1.35 +- 0.35) z, very similar to cluster early-type galaxies. After correcting for luminosity evolution, the FP of field early-type galaxies has a scatter 0.09 +- 0.02 in log r_e, similar to that in local clusters. The scatter appears to be driven by low mass S0 galaxies; for the elliptical galaxies alone we find 0.03 +- 0.03. There is a hint that the FP has a different slope than in clusters, but more data are needed to confirm this. The similarity of the M/L ratios of cluster and field early-type galaxies provides a constraint on the relative ages of their stars. At = 0.43, field early-type galaxies are younger than cluster early-type galaxies by only 21 +- 13 %, and we infer that the stars in field early-type galaxies probably formed at z >~ 1.5. Recent semi-analytical models for galaxy formation in a Lambda-CDM Universe predict a systematic difference between field and cluster galaxies of Δ(ln M/L_B) ~ -0.6, much larger than the observed difference. This result is consistent with the hypothesis that field early-type galaxies formed earlier than predicted by these models.

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arXiv2001

The Evolution of Balmer Absorption Line Strengths in E/S0 Galaxies from z=0 to z=0.83

We present new results from a systematic study of absorption line strengths of galaxies in clusters approaching redshifts of unity. In this paper, we specifically compare the strengths of the high-order Balmer absorption features of Hgamma and Hdelta in E/S0s in the four clusters Abell 2256 (z=0.06), CL1358+62 (z=0.33), MS2053--04 (z=0.58), and MS1054--03 (z=0.83). By comparing the correlation of Balmer line strength with velocity dispersion for E/S0s in the three clusters, we find moderate evolution in the zero-point of the (Hdelta_A+Hgamma_A)-sigma relation with redshift. The trend is consistent with passive evolution of old stellar populations. Under the assumption that the samples can be compared directly, we use single-burst stellar population synthesis models to constrain the last major occurrences of star-formation in the observed E/S0s to be z_f > 2.5 (95% confidence). We have compared the evolution of the Balmer absorption with the evolution of the B-band fundamental plane and find that simple stellar population models agree very well with the data. While the best agreement occurs with a low value for Omega_m, the data provide strong confirmation of the time-evolution in recent stellar population models.

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arXiv2000

HST Photometry and Keck Spectroscopy of the Rich Cluster MS1054-03: Morphologies, Butcher-Oemler Effect and the Color-Magnitude Relation at z=0.83

We present a study of 81 I selected, spectroscopically-confirmed members of the X-ray cluster MS1054-03 at z=0.83. Redshifts and spectral types were determined from Keck spectroscopy. Morphologies and accurate colors were determined from a large mosaic of HST WFPC2 images in F606W and F814W. Early-type galaxies constitute only 44% of this galaxy population. Thirty-nine percent are spiral galaxies, and 17% are mergers. The early-type galaxies follow a tight and well-defined color-magnitude relation, with the exception of a few outliers. The observed scatter is 0.029 +- 0.005 magnitudes in restframe U-B. Most of the mergers lie close to the CM relation defined by the early-type galaxies. They are bluer by only 0.07 +- 0.02 magnitudes, and the scatter in their colors is 0.07 +- 0.04 magnitudes. Spiral galaxies in MS1054-03 exhibit a large range in their colors. The bluest spiral galaxies are 0.7 magnitudes bluer than the early-type galaxies, but the majority is within +- 0.2 magnitudes of the early-type galaxy sequence. The red colors of the mergers and the majority of the spiral galaxies are reflected in the fairly low Butcher-Oemler blue fraction of MS1054-03: f_B=0.22 +- 0.05. The slope and scatter of the CM relation of early-type galaxies are roughly constant with redshift, confirming previous studies that were based on ground-based color measurements and very limited membership information. However, the scatter in the combined sample of early-type galaxies and mergers is twice as high as the scatter of the early-type galaxies alone. This is a direct demonstration of the ``progenitor bias'': high redshift early-type galaxies seem to form a homogeneous, old population because the progenitors of the youngest present-day early-type galaxies are not included in the sample.

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arXiv1999

The Evolution of Early-Type Galaxies in Distant Clusters I.: Surface Photometry and Structural Parameters for 53 Galaxies in the z=0.33 Cluster CL1358+62

Using HST imaging of CL1358+62 (z=0.33) structural parameters are derived for 53 cluster members. We fit integrated r^{1/4}-laws to the integrated S.B. profiles, and fit two-dimensional r^{1/4}-law model galaxies to the images directly. The results from the two methods agree very well, with an rms scatter of 13% in r_e. The half-light radii range from 1 to 20 kpc, with a median of 3 kpc. We compared r_e from the r^{1/4}-law fits to r_{1/2} derived using other profiles. In particular, we fit Sersic r^{1/n}-laws and superpositions of r^{1/4}-law bulges with exponential disks. The r_{1/2} derived from the best-fit Sersic profiles varied with respect to r_e from the r^{1/4}-law fits by 1% in the median, but with a standard deviation of more than 40%. For the bulge-plus-disk fits, the derived r_{1/2} were offset from r_e of the r^{1/4}-law fits by 10% in the mean, also with a standard deviation of more than 40%. By comparing the Sersic r_{1/2} with those derived from the bulge-plus-disk fitting, that scatter is also large, at 30%. We conclude that r_{1/2} is generally measured with a typical accuracy of 30-40%. The large uncertainties in r_{1/2} do not impact the fundamental plane analysis because the combination r ^{0.76}, which enters the fundamental plane, is extremely stable. The rms scatter in r ^{0.76} is less than 3%, regardless of the form of the profile fit to the galaxies. We find that the median bulge fraction of the sample is 84% and that the few E+A galaxies in this sample have disks which make up about 10-35% of their total light. These results are consistent with residuals from fitting 2D r^{1/4}-law models directly to the galaxies, in which disk-like structures are revealed in about half of the sample. Two of the three E+A galaxies show spiral arm structure.

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arXiv1999

A Database of Cepheid Distance Moduli and TRGB, GCLF, PNLF and SBF Data Useful for Distance Determinations

We present a compilation of Cepheid distance moduli and data for four secondary distance indicators that employ stars in the old stellar populations: the planetary nebula luminosity function (PNLF), the globular cluster luminosity function (GCLF), the tip of the red giant branch (TRGB), and the surface brightness fluctuation (SBF) method. The database includes all data published as of July 15, 1999. The main strength of this compilation resides in all data being on a consistent and homogeneous system: all Cepheid distances are derived using the same calibration of the period-luminosity relation, the treatment of errors is consistent for all indicators, measurements which are not considered reliable are excluded. As such, the database is ideal for inter-comparing any of the distance indicators considered, or for deriving a Cepheid calibration to any secondary distance indicator. Specifically, the database includes: 1) Cepheid distances, extinctions and metallicities; 2) apparent magnitudes of the PNLF cutoff; 3) apparent magnitudes and colors of the turnover of the GCLF (both in the V- and B-bands); 4) apparent magnitudes of the TRGB (in the I-band) and V-I colors at and 0.5 magnitudes fainter than the TRGB; 5) apparent surface brightness fluctuation magnitudes I, K', K_short, and using the F814W filter with the HST/WFPC2. In addition, for every galaxy in the database we give reddening estimates from DIRBE/IRAS as well as HI maps, J2000 coordinates, Hubble and T-type morphological classification, apparent total magnitude in B, and systemic velocity. (Abridged)

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arXiv1999

The Hubble Space Telescope Key Project on the Extragalactic Distance Scale XXIV: The Calibration of Tully-Fisher Relations and the Value of the Hubble Constant

This paper presents the calibration of BVRIH$ Tully-Fisher relations based on Cepheid distances to 21 galaxies within 25 Mpc, and 23 clusters within 10,000 km/s. These relations have been applied to several distant cluster surveys in order to derive a value for the Hubble constant, H0, mainly concentrating on an I-band all-sky survey by Giovanelli and collaborators which consisted of total I magnitudes and 50% linewidth data for ~550 galaxies in 16 clusters. For comparison, we also derive the values of H0 using surveys in B-band and V-band by Bothun and collaborators, and in H-band by Aaronson and collaborators. Careful comparisons with various other databases from literature suggest that the H-band data, whose magnitudes are isophotal magnitudes extrapolated from aperture magnitudes rather than total magnitudes, are subject to systematic uncertainties. Taking a weighted average of the estimates of Hubble constants from four surveys, we obtain H0 = 71 +- 4 (random) +- 7 (systematic) km/s/Mpc. We have also investigated how various systematic uncertainties affect the value of H0 such as the internal extinction correction method used, Tully-Fisher slopes and shapes, a possible metallicity dependence of the Cepheid period-luminosity relation and cluster population incompleteness bias.

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arXiv1999

The Extragalactic Distance Scale Key Project XXVII. A Derivation of the Hubble Constant Using the Fundamental Plane and Dn-Sigma Relations in Leo I, Virgo, and Fornax

Using published photometry and spectroscopy, we construct the fundamental plane and D_n-Sigma relations in Leo I, Virgo and Fornax. The published Cepheid P-L relations to spirals in these clusters fixes the relation between angular size and metric distance for both the fundamental plane and D_n-Sigma relations. Using the locally calibrated fundamental plane, we infer distances to a sample of clusters with a mean redshift of cz \approx 6000 \kms, and derive a value of H_0=78+- 5+- 9 km/s/Mpc (random, systematic) for the local expansion rate. This value includes a correction for depth effects in the Cepheid distances to the nearby clusters, which decreased the deduced value of the expansion rate by 5% +- 5%. If one further adopts the metallicity correction to the Cepheid PL relation, as derived by the Key Project, the value of the Hubble constant would decrease by a further 6%+- 4%. These two sources of systematic error, when combined with a +- 6% error due to the uncertainty in the distance to the Large Magellanic Cloud, a +- 4% error due to uncertainties in the WFPC2 calibration, and several small sources of uncertainty in the fundamental plane analysis, combine to yield a total systematic uncertainty of +- 11%. We find that the values obtained using either the CMB, or a flow-field model, for the reference frame of the distant clusters, agree to within 1%. The Dn-Sigma relation also produces similar results, as expected from the correlated nature of the two scaling relations. A complete discussion of the sources of random and systematic error in this determination of the Hubble constant is also given, in order to facilitate comparison with the other secondary indicators being used by the Key Project.

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arXiv1999

The Evolution of Stellar Populations in Intermediate Redshift Clusters

The $M/L$ ratios and absorption line-strengths of distant cluster galaxies can be used to directly study their stellar populations, determine their redshift of formation, their scatter in ages, and any dependence of their ages on such internal properties such as velocity dispersion or mass. Comparing the zero-point the fundamental plane in the $z=0.33$ cluster CL1358+62 to that in Coma, we conclude that the redshift of formation for the stars in massive cluster E/S0s was $z\ga 2$. The fundamental plane in CL1358+62 has the following form: $r_e \propto σ^{1.31\pm 0.13}< I>_e^{-0.86\pm 0.10}$, indicating that the last epoch of star-formation has very little dependence on galaxy mass. The scatter in the CL1358+62 fundamental plane is also very low, equivalent to a scatter in ages of $\sim 15%$.We have also analyzed the $M/L_V$ ratios of galaxies of type S0/a and later. These early-type spirals follow a different plane from the E and S0 galaxies, with a scatter that is twice as large as the scatter for the E/S0s. These residuals also correlate with the residuals from the color-magnitude relation. Preliminary analysis of the absorption line-strengths of the CL1358+62 early-types indicate that they are well-described by uniformly old, single-burst stellar populations with metallicity varying as a function of velocity dispersion.

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arXiv1999

The HST Key Project on the Extragalactic Distance Scale XXVI. The Calibration of Population II Secondary Distance Indicators and the Value of the Hubble Constant

A Cepheid-based calibration is derived for four distance indicators that utilize stars in the old stellar populations: the tip of the red giant branch (TRGB), the planetary nebula luminosity function (PNLF), the globular cluster luminosity function (GCLF) and the surface brightness fluctuation method (SBF). The calibration is largely based on the Cepheid distances to 18 spiral galaxies within cz =1500 km/s obtained as part of the HST Key Project on the Extragalactic Distance Scale, but relies also on Cepheid distances from separate HST and ground-based efforts. The newly derived calibration of the SBF method is applied to obtain distances to four Abell clusters in the velocity range between 3800 and 5000 km/s, observed by Lauer et al. (1998) using the HST/WFPC2. Combined with cluster velocities corrected for a cosmological flow model, these distances imply a value of the Hubble constant of H0 = 69 +/- 4 (random) +/- 6 (systematic) km/s/Mpc. This result assumes that the Cepheid PL relation is independent of the metallicity of the variable stars; adopting a metallicity correction as in Kennicutt et al. (1998), would produce a (5 +/- 3)% decrease in H0. Finally, the newly derived calibration allows us to investigate systematics in the Cepheid, PNLF, SBF, GCLF and TRGB distance scales.

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