ABSTRACT: Recent observations have shown that compact nuclear star clusters (NSCs) are
present in up to 80% of galaxies. However, detailed studies of their dynamical
and chemical properties are confined mainly to spiral galaxy hosts, where they
are more easily observed. In this paper we present our study of the NSC in FCC
277, a nucleated elliptical galaxy in the Fornax cluster. We use a combination
of adaptive optics assisted near-infrared integral field spectroscopy, Hubble
Space Telescope imaging, and literature long slit data. We show that while the
NSC does not appear to rotate within our detection limit of ~6 km/s, rotation
is detected at larger radii, where the isophotes appear to be disky, suggesting
the presence of a nuclear disk. We also observe a distinct central velocity
dispersion drop that is indicative of a dynamically cold rotating sub-system.
Following the results of orbit-based dynamical modelling, co-rotating as well
as counter-rotating stellar orbits are simultaneously needed to reproduce the
observed kinematics. We find evidence for varying stellar populations, with the
NSC and nuclear disk hosting younger and more metal rich stars than the main
body of the galaxy. We argue that gas dissipation and some level of merging
have likely played an important role in the formation of the nucleus of this
intermediate-mass galaxy. This is in contrast to NSCs in low-mass early- type
galaxies, which may have been formed primarily through the infall of star
ABSTRACT: We present an investigation into the origins of a series of interlaced narrow
filamentary stellar structures, loops and plumes in the vicinity of the Virgo
Cluster, edge-on spiral galaxy, NGC 4216 that were previously identified by the
Blackbird Telescope. Using the deeper, higher-resolution and precisely
calibrated optical CFHT/MegaCam images obtained as part of the Next Generation
Virgo Cluster Survey (NGVS), we confirm the previously identified features and
identify a few additional structures. The NGVS data allowed us to make a
physical study of these low-surface brightness features and investigate their
origin. The likely progenitors of the structures were identified as either
already catalogued VCC dwarfs or newly discovered satellites caught in the act
of being destroyed. They have the same g-i color index and likely contain
similar stellar populations. The alignment of three dwarfs along an apparently
single stream is intriguing, and we cannot totally exclude that these are
second-generation dwarf galaxies being born inside the filament from the debris
of an original dwarf. The observed complex structures, including in particular
a stream apparently emanating from a satellite of a satellite, point to a high
rate of ongoing dwarf destruction/accretion in the region of the Virgo Cluster
where NGC 4216 is located. We discuss the age of the interactions and whether
they occurred in a group that is just falling into the cluster and shows signs
of so-called "pre-processing" before it gets affected by the cluster
environment, or in a group which already ventured towards the central regions
of Virgo Cluster.
ABSTRACT: The Advanced Camera for Surveys (ACS) Fornax Cluster Survey is a Hubble Space
Telescope program to image 43 early-type galaxies in the Fornax cluster, using
the F475W and F850LP bandpasses of the ACS. We employ both 1D and 2D techniques
to characterize the properties of the stellar nuclei in these galaxies, defined
as the central "luminosity excesses" relative to a Sersic model fitted to the
underlying host. We find 72+/-13% of our sample (31 galaxies) to be nucleated,
with only three of the nuclei offset by more than 0.5" from their galaxy
photocenter, and with the majority of nuclei having colors bluer than their
hosts. The nuclei are observed to be larger, and brighter, than typical Fornax
globular clusters, and to follow different structural scaling relations. A
comparison of our results to those from the ACS Virgo Cluster Survey reveals
striking similarities in the properties of the nuclei belonging to these
different environments. We briefly review a variety of proposed formation
models and conclude that, for the low-mass galaxies in our sample, the most
important mechanism for nucleus growth is probably infall of star clusters
through dynamical friction, while for higher mass galaxies, gas accretion
triggered by mergers, accretions and tidal torques is likely to dominate, with
the relative importance of these two processes varying smoothly as a function
of galaxy mass. Some intermediate-mass galaxies in our sample show a complexity
in their inner structure that may be the signature of "hybrid nuclei" that
arose through parallel formation channels.
ABSTRACT: Context: We study the peculiar interacting galaxy system of VCC1249/M49
located in the core of the Virgo B subcluster. Owing to a recent interaction
between the dwarf galaxy VCC1249 and the halo gas of the gE M49, neutral
hydrogen has been displaced from the interstellar medium of this dwarf into the
Virgo ICM. Observations also reveal multiple compact star-forming regions that
are embedded in this HI cloud, with a projected separation up to 13 kpc from
VCC1249 in the northwest direction.
Aims: Motivated by recent NUV imaging from GUViCS of the VCC1249/M49 system
that shows significant ongoing/recent star formation in the compact regions, we
aim to constrain the origin of these outlying HII regions with a
Methods: Using deep optical (u, g, i, z) imaging from NGVS and new Halpha
imaging obtained at the San Pedro Martir observatory together with Keck
long-slit spectroscopy, we characterize the SFR, ages, and metallicity of
VCC1249 and its outlying compact regions. Moreover, we analyze the color and
luminosity profile of the galaxy to investigate its recent interaction with
Results: Our new observations indicate that VCC1249 underwent a recent
interaction with M49 in which both ram-pressure stripping and tidal interaction
occured. The joint action of the two mechanisms led to the removal of the HI
gas from the ISM of VCC1249, while the gravitational tides triggered the
stellar tail and counter-tail of VCC1249. Our SED analysis reveals that the
star formation in this galaxy was truncated around 200 Myr ago and that the
outlying HII regions were born in situ about 10 Myr ago out of pre-enriched gas
removed from the dwarf galaxy. These observations also reveal that interactions
between central and satellite galaxies similar to the one between VCC1249/M49
may be an effective way of dispersing metals into the halos of massive
ABSTRACT: We combine new Wide Field Camera 3 IR Channel (WFC3/IR) F160W (H 160) imaging data for NGC 1399, the central galaxy in the Fornax cluster, with archival F475W (g 475), F606W (V 606), F814W (I 814), and F850LP (z 850) optical data from the Advanced Camera for Surveys (ACS). The purely optical g 475 – I 814, V 606 – I 814, and g 475 – z 850 colors of NGC 1399's rich globular cluster (GC) system exhibit clear bimodality, at least for magnitudes I 814 > 21.5. The optical-IR I 814 – H 160 color distribution appears unimodal, and this impression is confirmed by mixture modeling analysis. The V 606 – H 160 colors show marginal evidence for bimodality, consistent with bimodality in V 606 – I 814 and unimodality in I 814 – H 160. If bimodality is imposed for I 814 – H 160 with a double Gaussian model, the preferred blue/red split differs from that for optical colors; these "differing bimodalities" mean that the optical and optical-IR colors cannot both be linearly proportional to metallicity. Consistent with the differing color distributions, the dependence of I 814 – H 160 on g 475 – I 814 for the matched GC sample is significantly nonlinear, with an inflection point near the trough in the g 475 – I 814 color distribution; the result is similar for the I 814 – H 160 dependence on g 475 – z 850 colors taken from the ACS Fornax Cluster Survey. These g 475 – z 850 colors have been calibrated empirically against metallicity; applying this calibration yields a continuous, skewed, but single-peaked metallicity distribution. Taken together, these results indicate that nonlinear color-metallicity relations play an important role in shaping the observed bimodal distributions of optical colors in extragalactic GC systems.
The Astrophysical Journal 01/2012; 746(1):88. · 6.02 Impact Factor
ABSTRACT: We combine new Wide Field Camera~3 IR Channel (WFC3/IR) F160W (H) imaging
data for NGC1399, the central galaxy in the Fornax cluster, with archival F475W
(g), F606W (V), F814W (I), and F850LP (z) optical data from the Advanced Camera
for Surveys (ACS). The purely optical g-I, V-I, and g-z colors of NGC1399's
rich globular cluster (GC) system exhibit clear bimodality, at least for
magnitudes $I_814 > 21.5$. The optical-IR I-H color distribution appears
unimodal, and this impression is confirmed by mixture modeling analysis. The
V-H colors show marginal evidence for bimodality, consistent with bimodality in
V-I and unimodality in I-H. If bimodality is imposed for I-H with a double
Gaussian model, the preferred blue/red split differs from that for optical
colors; these "differing bimodalities" mean that the optical and optical-IR
colors cannot both be linearly proportional to metallicity. Consistent with the
differing color distributions, the dependence of I-H on g-I for the matched GC
sample is significantly nonlinear, with an inflection point near the trough in
the g-I color distribution; the result is similar for the I-H dependence on g-z
colors taken from the ACS Fornax Cluster Survey. These g-z colors have been
calibrated empirically against metallicity; applying this calibration yields a
continuous, skewed, but single-peaked metallicity distribution. Taken together,
these results indicate that nonlinear color-metallicity relations play an
important role in shaping the observed bimodal distributions of optical colors
in extragalactic GC systems.
ABSTRACT: We use the largest homogeneous sample of globular clusters (GCs), drawn from the ACSVCS and ACSFCS, to investigate the color gradients of GC systems in 76 early-type galaxies. We find that most GC systems possess an obvious negative gradient in g-z color (bluer outwards). For GC systems displaying color bimodality, both metal-rich and metal-poor GC subpopulations present shallower but significant color gradients on average, and the mean gradients of these two subpopulations are of roughly equal strength. The FOV of ACS mainly restricts us to measuring the inner gradients of GC systems. These gradients, however, can introduce an aperture bias when measuring the mean colors of GC subpopulations from relatively narrow central pointings. Inferred corrections to previous work imply a reduced significance for the relation between the mean color of metal-poor GCs and their host galaxy luminosity. The GC color gradients also show a dependence with host galaxy mass where the gradiens are weakest at the ends of the mass spectrum--in massive galaxies and dwarf galaxies--and strongest in galaxies of intermediate mass, around a stellar mass of M_stellar~10^10M_sun. We also measure color gradients for field stars in the host galaxies. We find that GC color gradients are systematically steeper than field star color gradients, but the shape of the gradient-mass relation is the same for both. If gradients are caused by rapid dissipational collapse and weakened by merging, these color gradients support a picture where the inner GC systems of most intermediate-mass and massive galaxies formed early and rapidly with the most massive galaxies having experienced greater merging. The lack of strong gradients in the GC systems of dwarfs, which probably have not experienced many recent major mergers, suggests that low mass halos were inefficient at retaining and mixing metals during the epoch of GC formation. Comment: 11 pages, 5 figures, Accepted for publication in ApJ
ABSTRACT: Although early observations with the Hubble Space Telescope (HST) pointed to a sharp dichotomy among early-type galaxies in terms of the logarithmic slope gamma' of their central surface brightness profiles, several studies in the past few years have called this finding into question. In particular, recent imaging surveys of 143 early-type galaxies belonging to the Virgo and Fornax Clusters using the Advanced Camera for Surveys (ACS) on board HST have not found a dichotomy in gamma', but instead a systematic progression from central luminosity deficit to excess relative to the inward extrapolation of the best-fitting global Sersic model. Given that earlier studies also found that the dichotomy persisted when analyzing the deprojected density profile slopes, we investigate the distribution of the three-dimensional luminosity density profiles of the ACS Virgo and Fornax Cluster Survey galaxies. Having fitted the surface brightness profiles with modified Sersic models, we then deproject the galaxies using an Abel integral and measure the inner slopes gamma_3D of the resulting luminosity density profiles at various fractions of the effective radius R_e. We find no evidence of a dichotomy, but rather, a continuous variation in the central luminosity profiles as a function of galaxy magnitude. We introduce a parameter, Delta_3D, that measures the central deviation of the deprojected luminosity profiles from the global Sersic fit, showing that this parameter varies smoothly and systematically along the luminosity function. Comment: 38 pages, 13 figures. Accepted for publication in ApJ
ABSTRACT: We measure surface brightness fluctuation (SBF) magnitudes in the F814W filter and (g 475 – I 814) colors for nine bright early-type Fornax cluster galaxies imaged with the Hubble Space Telescope Advanced Camera for Surveys (ACS). The goal is to achieve the first systematic SBF calibration for the ACS/F814W bandpass. Because of its much higher throughput, F814W is more efficient for SBF studies of distant galaxies than the ACS/F850LP bandpass that has been used to study nearby systems. Over the color range spanned by the sample galaxies, 1.06 < (g 475 – I 814) < 1.32 (AB mag), the dependence of SBF magnitude on (g 475 – I 814) is linear to a good approximation, with slope ~2. When the F850LP SBF distance measurements from the ACS Fornax Cluster Survey are used to derive absolute magnitudes, the dependence on (g 475 – I 814) becomes extremely tight, with a slope of 1.8 ± 0.2 and a scatter of 0.03 mag. The small observed scatter indicates both that the estimated random errors are correct and that the intrinsic deviations from the SBF-color relation are strongly correlated between the F814W and F850LP bandpasses, as expected. The agreement with predictions from stellar population models is good, both in slope and zero point, indicating that our mean Fornax distance of 20 Mpc is accurate. The models predict curvature in the relation beyond the color limits of our sample; thus, the linear calibration should not be extrapolated naively. In the appendices, we reconsider the Tonry ground-based and Jensen NICMOS SBF distance catalogs; we provide a correction formula to ameliorate the small apparent bias in the former and the offset needed to make the latter consistent with other SBF studies. We also tabulate two new SBF distances to galaxies observed in the ACS Virgo Cluster Survey.
The Astrophysical Journal 11/2010; 724(1):657. · 6.02 Impact Factor
ABSTRACT: We use a highly homogeneous set of data from 132 early-type galaxies in the Virgo and Fornax clusters in order to study the properties of the globular cluster luminosity function (GCLF). The globular cluster system of each galaxy was studied using a maximum likelihood approach to model the intrinsic GCLF after accounting for contamination and completeness effects. The results presented here update our Virgo measurements and confirm our previous results showing a tight correlation between the dispersion of the GCLF and the absolute magnitude of the parent galaxy. Regarding the use of the GCLF as a standard candle, we have found that the relative distance modulus between the Virgo and Fornax clusters is systematically lower than the one derived by other distance estimators, and in particular, it is 0.22 mag lower than the value derived from surface brightness fluctuation measurements performed on the same data. From numerical simulations aimed at reproducing the observed dispersion of the value of the turnover magnitude in each galaxy cluster we estimate an intrinsic dispersion on this parameter of 0.21 mag and 0.15 mag for Virgo and Fornax, respectively. All in all, our study shows that the GCLF properties vary systematically with galaxy mass showing no evidence for a dichotomy between giant and dwarf early-type galaxies. These properties may be influenced by the cluster environment as suggested by cosmological simulations.
The Astrophysical Journal 06/2010; 717(2):603. · 6.02 Impact Factor
ABSTRACT: We measure the half-light radii of globular clusters (GCs) in 43 galaxies from the Advanced Camera for Surveys (ACS) Fornax Cluster Survey. We use these data to extend previous work in which the environmental dependencies of the half-light radii of GCs in early-type galaxies in the ACS Virgo Cluster Survey were studied, and a corrected mean half-light radius (corrected for the observed environmental trends) was suggested as a reliable distance indicator. This work both increases the sample size for the study of the environmental dependencies, and adds leverage to the study of the corrected half-light radius as a possible distance indicator (since Fornax lies at a larger distance than the Virgo cluster). We study the environmental dependencies of the size of GCs using both a Principal Component Analysis as well as two-dimensional scaling relations. We largely confirm the environmental dependencies shown in Jordán et al., but find evidence that there is a residual correlation in the mean half-light radius of GC systems with galaxy magnitude, and subtle differences in the other correlations—so there may not be a universal correction for the half-light radii of lower luminosity galaxy GC systems. The main factor determining the size of a GC in an early-type galaxy is the GC color. Red GCs have rh = 2.8 ± 0.3 pc, while blue GCs have rh = 3.4 ± 0.3 pc. We show that for bright early-type galaxies (MB < –19 mag), the uncorrected mean half-light radius of the GC system is by itself an excellent distance indicator (with error ~11%), having the potential to reach cosmologically interesting distances in the era of high angular resolution adaptive optics on large optical telescopes.
The Astrophysical Journal 05/2010; 715(2):1419. · 6.02 Impact Factor
ABSTRACT: We measure the half-light radii of globular clusters (GCs) in 43 galaxies from the ACS Fornax Cluster Survey (ACSFCS). We use these data to extend previous work in which the environmental dependencies of the half-light radii of GCs in early type galaxies in the ACS Virgo Cluster Survey (ACSVCS) were studied, and a corrected mean half-light radius (corrected for the observed environmental trends) was suggested as a reliable distance indicator. This work both increases the sample size for the study of the environmental dependencies, and adds leverage to the study of the corrected half-light radius as a possible distance indicator (since Fornax lies at a larger distance than the Virgo cluster). We study the environmental dependencies of the size of GCs using both a Principal Component Analysis as well as 2D scaling relations. We largely confirm the environmental dependencies shown in Jordan et al. (2005), but find evidence that there is a residual correlation in the mean half-light radius of GC systems with galaxy magnitude, and subtle differences in the other correlations - so there may not be a universal correction for the half-light radii of lower luminosity galaxy GC systems. The main factor determining the size of a GC in an early type galaxy is the GC color. Red GCs have = 2.8+/-0.3 pc, while blue GCs have = 3.4+/-0.3 pc. We show that for bright early-type galaxies (M_B < -19 mag), the uncorrected mean half-light radius of the GC system is by itself an excellent distance indicator (with error ~11%), having the potential to reach cosmologically interesting distances in the era of high angular resolution adaptive optics on large optical telescopes. Comment: ApJ in press, 19 pages, 16 figures.
ABSTRACT: We investigate the color-magnitude relation for globular clusters (GCs)—the so-called blue tilt—detected in the Advanced Camera for Surveys (ACS) Fornax Cluster Survey and using the combined sample of GCs from the ACS Fornax and Virgo Cluster Surveys. We find a tilt of γ z ≡ d(g – z)/dz = –0.0257 ± 0.0050 for the full GC sample of the Fornax Cluster Survey (5800 GCs). This is slightly shallower than the value γ z = –0.0459 ± 0.0048 found for the Virgo Cluster Survey GC sample (11,100 GCs). The slope for the merged Fornax and Virgo data sets (16,900 GCs) is γ z = –0.0293 ± 0.0085, corresponding to a mass-metallicity relation of Z M 0.43±0.12. We find that the blue tilt sets in at masses in excess of M ~ 2 × 105 M ☉. The tilt is stronger for GCs belonging to high-mass galaxies (M * 5 × 1010 M ☉) than for those in low-mass galaxies (M * 5 × 1010 M ☉). It is also more pronounced for GCs with smaller galactocentric distances. Our findings suggest a range of mass-metallicity relations Z GC M 0.3-0.7 GC which vary as a function of host galaxy mass/luminosity, a scaling similar to that observed for dwarf spheroidal galaxies. We compare our observations to a recent model of star cluster self-enrichment with generally favorable results. We suggest that, within the context of this model, the protocluster clouds out of which the GCs formed may have had density profiles slightly steeper than isothermal and/or star formation efficiencies somewhat below 0.3. We caution, however, that the significantly different appearance of the color-magnitude diagrams (CMDs) defined by the GC systems associated with galaxies of similar mass and morphological type poses a challenge to any single mechanism, including self-enrichment, that seeks to explain generically the observed GC color-magnitude relations. We therefore suggest that the detailed (and stochastic) merger/accretion histories of individual galaxies have likely played a non-negligible role determining the distribution of GCs in the CMDs of individual GC systems.
The Astrophysical Journal 02/2010; 710(2):1672. · 6.02 Impact Factor
ABSTRACT: Metal-poor globular clusters (GCs) are our local link to the earliest epochs of star formation and galaxy building. Studies of extragalactic GC systems using deep, high-quality imaging have revealed a small but significant slope to the color-magnitude relation for metal-poor GCs in a number of galaxies. We present a study of the M87 GC system using deep, archival HST/ACS imaging with the F606W and F814W filters, in which we find a significant color-magnitude relation for the metal-poor GCs. The slope of this relation in the I versus V-I color-magnitude diagram (γ I = –0.024 ± 0.006) is perfectly consistent with expectations based on previously published results using data from the ACS Virgo Cluster Survey. The relation is driven by the most luminous GCs, those with MI –10, and its significance is largest when fitting metal-poor GCs brighter than MI = –7.8, a luminosity which is ~1 mag fainter than our fitted Gaussian mean for the luminosity function (LF) of blue, metal-poor GCs (~0.8 mag fainter than the mean for all GCs). These results indicate that there is a mass scale at which the correlation begins, and is consistent with a scenario where self-enrichment drives a mass-metallicity relationship. We show that previously measured half-light radii of M87 GCs from best-fit PSF-convolved King models are consistent with the more accurate measurements in this study, and we also explain how the color-magnitude relation for metal-poor GCs is real and cannot be an artifact of the photometry. We fit Gaussian and evolved Schechter functions to the luminosity distribution of GCs across all colors, as well as divided into blue and red subpopulations, finding that the blue GCs have a brighter mean luminosity and a narrower distribution than the red GCs. Finally, we present a catalog of astrometry and photometry for 2250 M87 GCs.
The Astrophysical Journal 08/2009; 703(1):42. · 6.02 Impact Factor
ABSTRACT: We present catalogs of globular cluster candidates for the 100 galaxies of the Advanced Camera for Surveys Virgo Cluster Survey, a large program to carry out imaging of early-type members of the Virgo Cluster using the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope. We describe the procedure used to select bona fide globular cluster candidates out of the full list of detections based on model-based clustering methods with the use of expected contamination catalogs constructed using blank field observations and which are customized for each galaxy. We also present the catalogs of expected contaminants for each of our target galaxies. For each detected source we measure its position, magnitudes in the F475W (≈ Sloan g) and F850LP (≈ Sloan z) bandpasses, and half-light radii by fitting point-spread function convolved King models to the observed light distribution. These measurements are presented for 20,375 sources, of which 12,763 are likely to be globular clusters. Finally, we detail the calculation of the aperture corrections adopted for the globular cluster photometry.
The Astrophysical Journal Supplement Series 02/2009; 180:54-66. · 13.46 Impact Factor
ABSTRACT: We present the V and I light curves of a nova discovered in the disk of the spiral galaxy M100, located in the Virgo Cluster. In spite of the fact that the light curve is not well sampled around maximum light and the reddening to the nova is not accurately known, by adopting the maximum magnitude versus rate of decline relation by Della Valle & Livio we derive a distance modulus to M100 of μ0 ~31.0 ± 0.3 mag, fully consistent with the Cepheid distance modulus of 31.04 ± 0.17 mag found by Ferrarese et al. from the same set of HST/WFPC2 data.
The Astrophysical Journal 01/2009; 468(2):L95. · 6.02 Impact Factor
ABSTRACT: We report of the discovery and properties of Cepheid variable stars in the barred spiral galaxy NGC 3351 which is a member of the Leo I group of galaxies. NGC 3351 is one of 18 galaxies being observed as part of the Hubble Space Telescope (HST) Key Project on the Extragalactic Distance Scale which aims to determine the Hubble constant to 10% accuracy. Our analysis is based on observations made with the Wide Field Planetary Camera 2 during 1994 and early 1995. The Leo I group contains several bright galaxies of diverse types and is very suitable for linking together a number of secondary calibrators which can be employed at much greater distances than the Cepheid variables. We identify 49 probable Cepheids within NGC 3351 in the period range 10-43 days which have been observed at 12 epochs with the F555W filter and 4 epochs using the F814W filter. The HST F555W and F814W data have been transformed to the Johnson V and Cousins I magnitude systems, respectively. Photometry has principally been carried out using the DAOPHOT/ALLFRAME package. Reference is made to parallel measurements being made with the DoPHOT package. Apparent period-luminosity functions for V and I have been constructed assuming values of μ0 = 18.50 ± 0.10 mag and E(B - V) = 0.10 mag for the distance modulus and reddening of the Large Magellanic Cloud. A true distance modulus of 30.01 ± 0.19 mag is derived corresponding to a distance of 10.05 ± 0.88 Mpc with a reddening E(V - I) = 0.15 mag. A comparison is made with distances estimated for other galaxies in the Leo I group using various distance indicators. There is good agreement with the surface brightness fluctuation and planetary nebula luminosity function methods as calibrated by the Cepheids in M31.
The Astrophysical Journal 01/2009; 477(2):535. · 6.02 Impact Factor
ABSTRACT: We report on the discovery of Cepheids in the field spiral galaxy NGC 3621, based on observations made with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope (HST). NGC 3621 is one of 18 galaxies observed as a part of the HST Key Project on the Extragalactic Distance Scale, which aims to measure the Hubble constant to 10% accuracy. Sixty-nine Cepheids with periods in the range 9-60 days were observed over 12 epochs using the F555W filter, and over four epochs using the F814W filter. The HST F555W and F814W data were transformed to the Johnson V and Kron-Cousins I magnitude systems, respectively. Photometry was performed using two independent packages, DAOPHOT II/ALLFRAME and DoPHOT. Period-luminosity relations in the V and I bands were constructed using 36 fairly isolated Cepheids present in our set of 69 variables. Extinction-corrected distance moduli relative to the LMC of 10.63 ± 0.09 and 10.56 ± 0.10 mag were obtained using the ALLFRAME and DoPHOT data, respectively. True distance moduli of 29.13 ± 0.18 and 29.06 ± 0.18 mag, corresponding to distances of 6.3 ± 0.7 and 6.1 ± 0.7 Mpc, were obtained by assuming values of μ0 = 18.50 ± 0.10 mag and E(V - I) = 0.13 mag for the distance modulus and reddening of the LMC, respectively.
The Astrophysical Journal 01/2009; 490(2):517. · 6.02 Impact Factor
ABSTRACT: We report on the discovery of 34 Cepheid variables in NGC 2090, with periods ranging between 5 and 58 days. Apparent V and I period-luminosity relations for Cepheids with P ≥ 10 days have been constructed, assuming a fiducial distance modulus, μ0, of 18.50 ± 0.10 mag and a reddening, E(B-V), of 0.10 mag for the Large Magellanic Cloud. Using the ALLFRAME photometry package, an inferred reddening of E(V-I) = 0.09 ± 0.02 mag (internal error) and a true distance modulus of 30.45 ± 0.16 (random) ± 0.16 (systematic) mag for NGC 2090 are found. The corresponding distance is 12.3 ± 0.9 (random) ± 0.9 (systematic) Mpc, a value that agrees at the 2.5% level with that derived from an independent analysis using a modified version of the DoPHOT photometry package.
The Astrophysical Journal 01/2009; 500(2):763. · 6.02 Impact Factor
ABSTRACT: The distance to NGC 7331 has been derived from Cepheid variables observed with the Hubble Space Telescope (HST) WFPC2, as part of the Extragalactic Distance Scale Key Project. Multiepoch exposures in F555W ( ~V) and F814W ( ~I), with photometry derived independently from DoPHOT and DAOPHOT/ALLFRAME programs, were used to detect a total of 13 reliable Cepheids, with periods between 11 and 42 days. The relative distance moduli between NGC 7331 and the LMC, derived from the V and I magnitudes, imply an extinction to NGC 7331 of AV = 0.47 ± 0.15 mag and an extinction-corrected distance modulus to NGC 7331 of 30.89 ± 0.14 (random), equivalent to a distance of 15.1+1.0−0.9 Mpc. There are additional systematic uncertainties in the distance modulus of ±0.12 mag resulting from the calibration of the Cepheid period-luminosity relation and a systematic offset of +0.05 ± 0.04 mag if the metallicity correction inferred from the M101 results of Kennicutt et al. are applied.
The Astrophysical Journal 01/2009; 501(1):32. · 6.02 Impact Factor