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[show abstract]
[hide abstract]
ABSTRACT: Distance measures on a coherent scale around the sky are required to address
the outstanding cosmological problems of the Hubble Constant and of departures
from the mean cosmic flow. The correlation between galaxy luminosities and
rotation rates can be used to determine distances to many thousands of galaxies
in a wide range of environments potentially out to 200 Mpc. Mid-infrared (3.6
microns) photometry with the Spitzer Space Telescope is particularly valuable
as the source of the luminosities because it provides products of uniform
quality across the sky. From a perch above the atmosphere, essentially the
total magnitude of targets can be registered in exposures of a few minutes.
Extinction is minimal and the flux is dominated by the light from old stars
which is expected to correlate with the mass of the targets.
In spite of the superior photometry, the correlation between mid-infrared
luminosities and rotation rates extracted from neutral hydrogen profiles is
slightly degraded from the correlation found with I band luminosities. A color
correction recovers a correlation that provides comparable accuracy to that
available at I band (~20% 1sigma in an individual distance) while retaining the
advantages identified above. Without the color correction the relation between
linewidth and [3.6] magnitudes is M^{b,i,k,a}_{[3.6]} = -20.34 - 9.74 (log
W_{mx}^{i} -2.5). This description is found with a sample of 213 galaxies in 13
clusters that define the slope and 26 galaxies with Cepheid or tip of the red
giant branch distances that define the zero point. A color corrected parameter
M_{C_{[3.6]}} is constructed that has reduced scatter: M_{C_{[3.6]}} = -20.34 -
9.13 (log W_{mx}^{i} -2.5). Consideration of the 7 calibration clusters beyond
50 Mpc, outside the domain of obvious peculiar velocities, provides a
preliminary Hubble Constant estimate of H_0=74+/-5 km/s/Mpc.
01/2013;
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[show abstract]
[hide abstract]
ABSTRACT: The Carnegie Hubble Program (CHP) is designed to calibrate the extragalactic
distance scale using data from the post-cryogenic era of the Spitzer Space
Telescope. The ultimate goal of the CHP is a systematic improvement in the
distance scale leading to a determination of the Hubble Constant to within an
accuracy of 2%. This paper focuses on the measurement and calibration of the
Galactic Cepheid Period-Luminosity (Leavitt) Relation using the warm Spitzer
IRAC 1 and 2 bands at 3.6 and 4.5 \mu m. We present photometric measurements
covering the period range 4 - 70 days for 37 Galactic Cepheids. Data at 24
phase points were collected for each star.
Three PL relations of the form M=a(Log(P)-1)+b are derived. The method
adopted here takes the slope a to be -3.31, as determined from the Spitzer LMC
data of Scowcroft et al. (2012). Using the geometric HST guide-star distances
to ten Galactic Cepheids we find a calibrated 3.6 micron PL zero-point of
-5.80\pm0.03. Together with our value for the LMC zero-point we determine a
reddening-corrected distance modulus of 18.48\pm0.04 mag to the LMC.
The mid-IR Period-Color diagram and the [3.6] - [4.5] color variation with
phase are interpreted in terms of CO absorption at 4.5 \mu m. This situation
compromises the use of the 4.5 \mu m data for distance determinations.
09/2012;
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[show abstract]
[hide abstract]
ABSTRACT: Using a mid-infrared calibration of the Cepheid distance scale based on
recent observations at 3.6 um with the Spitzer Space Telescope, we have
obtained a new, high-accuracy calibration of the Hubble constant. We have
established the mid-IR zero point of the Leavitt Law (the Cepheid
Period-Luminosity relation) using time-averaged 3.6 um data for ten
high-metallicity, Milky Way Cepheids having independently-measured
trigonometric parallaxes. We have adopted the slope of the PL relation using
time-averaged 3.6 um data for 80 long-period Large Magellanic Cloud (LMC)
Cepheids falling in the period range 0.8 < log(P) < 1.8. We find a new
reddening-corrected distance to the LMC of 18.477 +/- 0.033 (systematic) mag.
We re-examine the systematic uncertainties in H0, also taking into account new
data over the past decade. In combination with the new Spitzer calibration, the
systematic uncertainty in H0 over that obtained by the Hubble Space Telescope
(HST) Key Project has decreased by over a factor of three. Applying the Spitzer
calibration to the Key Project sample, we find a value of H0 = 74.3 with a
systematic uncertainty of +/-2.1 (systematic) km/s/Mpc, corresponding to a 2.8%
systematic uncertainty in the Hubble constant. This result, in combination with
WMAP7 measurements of the cosmic microwave background anisotropies and assuming
a flat universe, yields a value of the equation of state for dark energy, w0 =
-1.09 +/- 0.10. Alternatively, relaxing the constraints on flatness and the
numbers of relativistic species, and combining our results with those of WMAP7,
Type Ia supernovae and baryon acoustic oscillations yields w0 = -1.08 +/- 0.10
and a value of N_eff = 4.13 +/- 0.67, mildly consistent with the existence of a
fourth neutrino species.
08/2012;
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ShiAnne Kattner,
Douglas C. Leonard,
Christopher R. Burns,
M. M. Phillips,
Gaston Folatelli,
Nidia Morrell,
Maximilian D. Stritzinger,
Mario Hamuy, Wendy L. Freedman,
Sven E. Persson,
Miguel Roth,
Nicholas B. Suntzeff
[show abstract]
[hide abstract]
ABSTRACT: We analyze the standardizability of Type Ia supernovae (SNe Ia) in the
near-infrared (NIR) by investigating the correlation between observed peak NIR
absolute magnitude and post-maximum B-band decline rate. A sample of 27
low-redshift SNe Ia observed by the Carnegie Supernova Project between 2004 to
2007 is used. All 27 objects have pre-maximum coverage in optical bands, with a
subset of 13 having pre-maximum NIR observations as well. We describe the
methods used to derive absolute peak magnitudes and decline rates from both
spline- and template-fitting procedures, and confirm prior findings that
fitting templates to SNe Ia light curves in the NIR is problematic due to the
diversity of post-maximum behaviour of objects that are characterized by
similar decline rate values, especially at high decline rates. Nevertheless, we
show that NIR light curves can be reasonably fit with a template, especially if
the observations begin within 5 days after NIR maximum. For the subset of 13
objects in our dataset that excludes the highly reddened and fast declining SNe
Ia, and includes only those objects for which NIR observations began prior to
five days after maximum light, we find modest evidence for a peak
luminosity-decline rate relation in Y, and stronger evidence in J and H. Using
Rv values differing from the canonical value of 3.1 is shown to have little
effect on the results. A Hubble diagram is presented for the NIR bands and the
B band. The resulting scatter for the combined NIR bands is 0.13 mag, while the
B band produces a scatter of 0.22 mag. The data suggest that applying a
correction to SNe Ia peak luminosities for decline rate is likely to be
beneficial in the J and H bands to make SNe Ia more precise distance
indicators, but of only marginal importance in the Y band.
01/2012;
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[show abstract]
[hide abstract]
ABSTRACT: We present a physically motivated explanation for the observed, monotonic increase in slope, and the simultaneous (and also monotonic) decrease in the width/scatter of the Leavitt law (the Cepheid period-luminosity (PL) relation) as one systematically moves from the blue and visual into the near- and mid-infrared. We calibrate the wavelength-dependent, surface-brightness sensitivities to temperature using the observed slopes of PL relations from the optical through the mid-infrared and test the calibration by comparing the theoretical predictions with direct observations of the wavelength dependence of the scatter in the Large Magellanic Cloud Cepheid PL relation. In doing so we find the slope of the period-radius (PR) relation is c = 0.724 ± 0.006. Investigating the effect of differential reddening suggests that this value may be overestimated by as much as 10%; however, the same slope of the PR relation fits the (very much unreddened) Cepheids in IC 1613, albeit with lower precision. The discussion given is general and also applies to RR Lyrae stars, which also show similarly increasing PL slopes and decreasing scatter with increasing wavelength.
The Astrophysical Journal 12/2011; 744(2):132. · 6.02 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We present a physically motivated explanation for the observed, monotonic
increase in slope, and the simultaneous (and also monotonic) decrease in the
width/scatter of the Leavitt Law (the Cepheid Period-Luminosity (PL) relation)
as one systematically moves from the blue and visual into the near and
mid-infared. We calibrate the wavelength-dependent, surface-brightness
sensitivities to temperature using the observed slopes of PL relations from the
optical through the mid-infrared, and test the calibration by comparing the
theoretical predictions with direct observations of the wavelength dependence
of the scatter in the Large Magellanic Cloud Cepheid PL relation. In doing so
we find the slope of the Period-Radius (PR) relation is c = 0.724 +/- 0.006.
Investigating the effect of differential reddening suggests that this value may
be overestimated by as much as 10%; however the same slope of the PR relation
fits the (very much unreddened) Cepheids in IC1613, albeit with lower
precision. The discussion given is general, and also applies to RR Lyrae stars,
which also show similarly increasing PL slopes and decreasing scatter with
increasing wavelength.
11/2011;
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[show abstract]
[hide abstract]
ABSTRACT: We present an overview of and preliminary results from an ongoing comprehensive program that has a goal of determining the Hubble constant to a systematic accuracy of ±2%. As part of this program, we are currently obtaining 3.6 μm data using the Infrared Array Camera on Spitzer, and the program is designed to include James Webb Space Telescope in the future. We demonstrate that the mid-infrared period-luminosity relation for Cepheids at 3.6 μm is the most accurate means of measuring Cepheid distances to date. At 3.6 μm, it is possible to minimize the known remaining systematic uncertainties in the Cepheid extragalactic distance scale. We discuss the advantages of 3.6 μm observations in minimizing systematic effects in the Cepheid calibration of H 0 including the absolute zero point, extinction corrections, and the effects of metallicity on the colors and magnitudes of Cepheids. We undertake three independent tests of the sensitivity of the mid-IR Cepheid Leavitt Law to metallicity, which when combined will allow a robust constraint on the effect. Finally, we provide a new mid-IR Tully-Fisher relation for spiral galaxies.
The Astronomical Journal 11/2011; 142(6):192. · 4.03 Impact Factor
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Maximilian D. Stritzinger,
M. M. Phillips,
Luis N. Boldt,
Chris Burns,
Abdo Campillay,
Carlos Contreras,
Sergio Gonzalez,
Gastón Folatelli,
Nidia Morrell,
Wojtek Krzeminski, [......],
Mario Hamuy, Wendy L. Freedman,
Barry F. Madore,
J. L. Marshall,
Sven E. Persson,
Jean-Philippe Rheault,
Nicholas B. Suntzeff,
Steven Villanueva,
Weidong Li,
and Alexei V. Filippenko
[show abstract]
[hide abstract]
ABSTRACT: The Carnegie Supernova Project (CSP) was a five-year observational survey conducted at Las Campanas Observatory that obtained, among other things, high-quality light curves of ~100 low-redshift Type Ia supernovae (SNe Ia). Presented here is the second data release of nearby SN Ia photometry consisting of 50 objects, with a subset of 45 having near-infrared follow-up observations. Thirty-three objects have optical pre-maximum coverage with a subset of 15 beginning at least five days before maximum light. In the near-infrared, 27 objects have coverage beginning before the epoch of B-band maximum, with a subset of 13 beginning at least five days before maximum. In addition, we present results of a photometric calibration program to measure the CSP optical (uBgVri) bandpasses with an accuracy of ~1%. Finally, we report the discovery of a second SN Ia, SN 2006ot, similar in its characteristics to the peculiar SN 2006bt.
The Astronomical Journal 10/2011; 142(5):156. · 4.03 Impact Factor
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Maximilian Stritzinger,
M. M. Phillips,
Luis Boldt S,
Chris Burns,
Abdo Campillay,
Carlos Contreras,
Sergio Gonzalez,
Gaston Folatelli,
Nidia Morrell,
Wojtek Krzeminski, [......],
Mario Hamuy, Wendy L. Freedman,
Barry Madore,
Jennifer L. Marshall,
Sven E. Persson,
Jean-Philippe Rheault,
Nicholas Suntzeff,
Steven Villanueva,
Weidong Li,
Alexei V. Filippenko
[show abstract]
[hide abstract]
ABSTRACT: The Carnegie Supernova Project (CSP) was a five-year observational survey
conducted at Las Campanas Observatory that obtained, among other things,
high-quality light curves of ~100 low-redshift Type Ia supernovae (SNe Ia).
Presented here is the second data release of nearby SN Ia photometry consisting
of 50 objects, with a subset of 45 having near-infrared follow-up observations.
Thirty-three objects have optical pre-maximum coverage with a subset of 15
beginning at least 5 days before maximum light. In the near-infrared, 27
objects have coverage beginning before the epoch of B-band maximum, with a
subset of 13 beginning at least 5 days before maximum. In addition, we present
results of a photometric calibration program to measure the CSP optical
(uBgVri)bandpasses with an accuracy of ~1%. Finally, we report the discovery of
a second SN Ia, SN 2006ot, similar in its characteristics to the peculiar SN
2006bt.
08/2011;
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[show abstract]
[hide abstract]
ABSTRACT: 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
(0.45-8.0um) as a function of spectroscopic [Fe/H] abundances of individual
Cepheids in the Large Magellanic Cloud from Romaniello et al. (2008). 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 cross-over occurring near the K band at about 2.2um,
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,
SMC and LMC, but is opposite in sign to most other empirical tests of the
sensitivity of Cepheid distances to mean [O/H] HII 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 Dmu_o = -0.17 (+/- 0.31) ([O/H] - 8.80) - 0.21
(+/-0.10). This is in agreement with previous determinations, but statistically
inconclusive.
03/2011;
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Christopher R. Burns,
Maximilian Stritzinger,
M. M. Phillips,
ShiAnne Kattner,
S. E. Persson,
Barry F. Madore, Wendy L. Freedman,
Luis Boldt,
Abdo Campillay,
Carlos Contreras,
Gaston Folatelli,
Sergio Gonzalez,
Wojtek Krzeminski,
Nidia Morrell,
Francisco Salgado,
and Nicholas B. Suntzeff
[show abstract]
[hide abstract]
ABSTRACT: In providing an independent measure of the expansion history of the universe, the Carnegie Supernova Project (CSP) has observed 71 high-z Type Ia supernovae (SNe Ia) in the near-infrared bands Y and J. These can be used to construct rest-frame i-band light curves which, when compared to a low-z sample, yield distance moduli that are less sensitive to extinction and/or decline-rate corrections than in the optical. However, working with NIR observed and i-band rest-frame photometry presents unique challenges and has necessitated the development of a new set of observational tools in order to reduce and analyze both the low-z and high-z CSP sample. We present in this paper the methods used to generate uBVgriYJH light-curve templates based on a sample of 24 high-quality low-z CSP SNe. We also present two methods for determining the distances to the hosts of SN Ia events. A larger sample of 30 low-z SNe Ia in the Hubble flow is used to calibrate these methods. We then apply the method and derive distances to seven galaxies that are so nearby that their motions are not dominated by the Hubble flow.
The Astronomical Journal 12/2010; 141(1):19. · 4.03 Impact Factor
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Maximilian Stritzinger,
Christopher R. Burns,
Mark M. Phillips,
Gastón Folatelli,
Kevin Krisciunas,
ShiAnne Kattner,
Sven E. Persson,
Luis Boldt,
Abdo Campillay,
Carlos Contreras,
Wojtek Krzeminski,
Nidia Morrell,
Francisco Salgado, Wendy L. Freedman,
Mario Hamuy,
Barry F. Madore,
Miguel Roth,
and Nicholas B. Suntzeff
[show abstract]
[hide abstract]
ABSTRACT: The giant elliptical galaxy NGC 1316 (Fornax A) is a well-studied member of the Fornax Cluster and a prolific producer of Type Ia supernovae (SNe Ia), having hosted four observed events since 1980. Here, we present detailed optical- and near-infrared light curves of the spectroscopically normal SN 2006dd. These data are used, along with previously published photometry of the normal SN 1980N and SN 1981D, and the fast-declining, low-luminosity SN 2006mr, to compute independent estimates of the host reddening for each SN, and the distance to NGC 1316. From the three normal SNe, we find a distance of 17.8 ± 0.3 (random) ± 0.3 (systematic) Mpc for Ho = 72. Distance moduli derived from the "EBV" and Tripp methods give the values that are mutually consistent with 4%-8%. Moreover, the weighted means of the distance moduli for these three SNe for three methods agree to within 3%. This consistency is encouraging and supports the premise that Type Ia SNe are reliable distance indicators at the 5% precision level or better. On the other hand, the two methods used to estimate the distance of the fast-declining SN 2006mr both yield a distance to NGC 1316 which is 25%-30% larger. This disparity casts doubt on the suitability of fast-declining events for estimating extragalactic distances. Modest-to-negligible host galaxy reddening values are derived for all four SNe. Nevertheless, two of them (SN 2006dd and SN 2006mr) show strong Na I D interstellar lines in the host galaxy system. The strength of this absorption is completely inconsistent with the small reddening values derived from the SN light curves if the gas in NGC 1316 is typical of that found in the interstellar medium of the Milky Way. In addition, the equivalent width of the Na lines in SN 2006dd appears to have weakened significantly some 100-150 days after explosion.
The Astronomical Journal 11/2010; 140(6):2036. · 4.03 Impact Factor
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Keren Sharon,
Avishay Gal-Yam,
Dan Maoz,
Alexei V. Filippenko,
Ryan J. Foley,
Jeffrey M. Silverman,
Harald Ebeling,
Cheng-Jiun Ma,
Eran O. Ofek,
Jean-Paul Kneib,
Megan Donahue,
Richard S. Ellis, Wendy L. Freedman,
Robert P. Kirshner,
John S. Mulchaey,
Vicki L. Sarajedini,
and G. Mark Voit
[show abstract]
[hide abstract]
ABSTRACT: Supernova (SN) rates are potentially powerful diagnostics of metal enrichment and SN physics, particularly in galaxy clusters with their deep, metal-retaining potentials and relatively simple star formation histories. We have carried out a survey for SNe in galaxy clusters, at a redshift range of 0.5 < z < 0.9, using the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope. We reimaged a sample of 15 clusters that were previously imaged by ACS, thus obtaining two to three epochs per cluster in which we discovered five likely cluster SNe, six possible cluster Type Ia supernovae, two hostless SN candidates, and several background and foreground events. Keck spectra of the host galaxies were obtained to establish cluster membership. We conducted detailed efficiency simulations, and measured the stellar luminosities of the clusters using Subaru images. We derive a cluster SN rate of 0.35SNu B +0.17 –0.12(statistical) ±0.13(classification) ±0.01(systematic) (where SNu B = SNe (100 yr 1010 L B,☉)–1) and 0.112SNu M +0.055 –0.039(statistical) ±0.042(classification) ±0.005(systematic) (where SNu M = SNe (100 yr 1010 M ☉)–1). As in previous measurements of cluster SN rates, the uncertainties are dominated by small-number statistics. The SN rate in this redshift bin is consistent with the SN rate in clusters at lower redshifts (to within the uncertainties), and shows that there is, at most, only a slight increase of cluster SN rate with increasing redshift. The low and fairly constant SN Ia rate out to z 1 implies that the bulk of the iron mass in clusters was already in place by z 1. The recently observed doubling of iron abundances in the intracluster medium between z = 1 and 0, if real, is likely to be the result of redistribution of existing iron, rather than new production of iron.
The Astrophysical Journal 07/2010; 718(2):876. · 6.02 Impact Factor
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Keren Sharon,
Avishay Gal-Yam,
Dan Maoz,
Alexei V. Filippenko,
Ryan J. Foley,
Jeffrey M. Silverman,
Harald Ebeling,
Cheng-Jiun Ma,
Eran O. Ofek,
Jean-Paul Kneib,
Megan Donahue,
Richard S. Ellis, Wendy L. Freedman,
Robert P. Kirshner,
John S. Mulchaey,
Vicki L. Sarajedini,
G. Mark Voit
[show abstract]
[hide abstract]
ABSTRACT: Supernova (SN) rates are potentially powerful diagnostics of metal enrichment and SN physics, particularly in galaxy clusters with their deep, metal-retaining potentials and relatively simple star-formation histories. We have carried out a survey for supernovae (SNe) in galaxy clusters, at a redshift range 0.5<z<0.9, using the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope. We reimaged a sample of 15 clusters that were previously imaged by ACS, thus obtaining two to three epochs per cluster, in which we discovered five likely cluster SNe, six possible cluster SNe Ia, two hostless SN candidates, and several background and foreground events. Keck spectra of the host galaxies were obtained to establish cluster membership. We conducted detailed efficiency simulations, and measured the stellar luminosities of the clusters using Subaru images. We derive a cluster SN rate of 0.35 SNuB +0.17/-0.12 (statistical) \pm0.13 (classification) \pm0.01 (systematic) [where SNuB = SNe (100 yr 10^10 L_B_sun)^-1] and 0.112 SNuM +0.055/-0.039 (statistical) \pm0.042 (classification) \pm0.005 (systematic) [where SNuM = SNe (100 yr 10^10 M_sun)^-1]. As in previous measurements of cluster SN rates, the uncertainties are dominated by small-number statistics. The SN rate in this redshift bin is consistent with the SN rate in clusters at lower redshifts (to within the uncertainties), and shows that there is, at most, only a slight increase of cluster SN rate with increasing redshift. The low and fairly constant SN Ia rate out to z~1 implies that the bulk of the iron mass in clusters was already in place by z~1. The recently observed doubling of iron abundances in the intracluster medium between z=1 and 0, if real, is likely the result of redistribution of existing iron, rather than new production of iron. Comment: Accepted to ApJ. Full resolution version available at http://kicp.uchicago.edu/~kerens/HSTclusterSNe/
06/2010;
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[show abstract]
[hide abstract]
ABSTRACT: We present a technique for decomposing Cepheid light curves into their fundamental constituent parts; that is, their radius and temperature variations. We demonstrate that any given pair of optical luminosity and color curves can be used to predict the shape, amplitude and phase of a Cepheid's light variation at any other wavelength. With such predictions in hand, a single new observation at any given new wavelength can be used to normalize the properties of the predicted light curve, and in specific, derive a precise value of the time-averaged mean. We suggest that this method will be of great advantage in efficiently observing and precisely obtaining the mean properties of known Cepheids scheduled to be observed at new wavelengths, specifically in the mid-infrared where JWST will be operating. Comment: Accepted to the ApJ; 16 pages, 7 figures
06/2010;
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[show abstract]
[hide abstract]
ABSTRACT: Considerable progress has been made in determining the Hubble constant over the past two decades. We discuss the cosmological context and importance of an accurate measurement of the Hubble constant, and focus on six high-precision distance-determination methods: Cepheids, tip of the red giant branch, maser galaxies, surface brightness fluctuations, the Tully-Fisher relation and Type Ia supernovae. We discuss in detail known systematic errors in the measurement of galaxy distances and how to minimize them. Our best current estimate of the Hubble constant is 73 +/-2 (random) +/-4 (systematic) km/s/Mpc. The importance of improved accuracy in the Hubble constant will increase over the next decade with new missions and experiments designed to increase the precision in other cosmological parameters. We outline the steps that will be required to deliver a value of the Hubble constant to 2% systematic uncertainty and discuss the constraints on other cosmological parameters that will then be possible with such accuracy. Comment: To be published in Annual Reviews of Astronomy and Astrophysics, Vol. 48, 2010, consisting of 79 pages, 13 figures, 2 tables
04/2010;
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Wendy L. Freedman,
Christopher R. Burns,
M. M. Phillips,
Pamela Wyatt,
S. E. Persson,
Barry F. Madore,
Carlos Contreras,
Gaston Folatelli,
E. Sergio Gonzalez,
Mario Hamuy, [......],
Hubert Lampeitl,
John Marriner,
R Pain,
Kathy Perrett,
N. Regnault,
Adam G. Riess,
Masao Sako,
Donald P. Schneider,
Mark Sullivan,
Michael Wood-Vasey
[show abstract]
[hide abstract]
ABSTRACT: The Carnegie Supernova Project (CSP) is designed to measure the luminosity
distance for Type Ia supernovae (SNe Ia) as a function of redshift, and to set
observational constraints on the dark energy contribution to the total energy
content of the Universe. The CSP differs from other projects to date in its
goal of providing an I-band {rest-frame} Hubble diagram. Here we present the
first results from near-infrared (NIR) observations obtained using the Magellan
Baade telescope for SNe Ia with 0.1 < z < 0.7. We combine these results with
those from the low-redshift CSP at z <0.1 (Folatelli et al. 2009). We present
light curves and an I-band Hubble diagram for this first sample of 35 SNe Ia
and we compare these data to 21 new SNe Ia at low redshift. These data support
the conclusion that the expansion of the Universe is accelerating. When
combined with independent results from baryon acoustic oscillations (Eisenstein
et al. 2005), these data yield Omega_m = 0.27 +/- 0.0 (statistical), and
Omega_DE = 0.76 +/- 0.13 (statistical) +/- 0.09 (systematic), for the matter
and dark energy densities, respectively. If we parameterize the data in terms
of an equation of state, w, assume a flat geometry, and combine with baryon
acoustic oscillations, we find that w = -1.05 +/- 0.13 (statistical) +/- 0.09
(systematic). The largest source of systematic uncertainty on w arises from
uncertainties in the photometric calibration, signaling the importance of
securing more accurate photometric calibrations for future supernova cosmology
programs. Finally, we conclude that either the dust affecting the luminosities
of SNe Ia has a different extinction law (R_V = 1.8) than that in the Milky Way
(where R_V = 3.1), or that there is an additional intrinsic color term with
luminosity for SNe Ia independent of the decline rate.
07/2009;
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[show abstract]
[hide abstract]
ABSTRACT: We report VRI CCD observations of nine Cepheids in the South Polar (Sculptor) Group spiral galaxy NGC 0247. Periods of these Cepheids range from 20 to 70 days. Over the past 20 years the very brightest Cepheid in our sample, NGC 0247:[MF09] C1, has decreased its period by 6%, faded by 0.8 mag in the V band, and become bluer by 0.23 mag in (V-I). A multi-wavelength analysis of the Cepheid data yields a true distance modulus of mod = 27.81 +/- 0.10 mag (3.36 +/- 0.16 Mpc) with a total line-of-sight reddening of E(V-I) = 0.07 +/-0.04 mag, after adopting an LMC true distance modulus of 18.5 mag and reddening of E(B-V) = 0.10 mag. These results are in excellent agreement with other very recently published (Cepheid and TRGB) distances to NGC 0247. Combining both Cepheid datasets gives mod_o = 27.85 +/-0.09 mag (3.72 +/- 0.15 Mpc) with E(V-I) = 0.11 +/- 0.03 mag.
02/2009;
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Maximilian Stritzinger,
Paolo Mazzali,
Mark M. Phillips,
Stefan Immler,
Alicia Soderberg,
Jesper Sollerman,
Luis Boldt,
Jonathan Braithwaite,
Peter Brown,
Christopher R. Burns, [......],
Sergio Gonzalez,
Mario Hamuy,
Wojtek Krzeminski,
Barry F. Madore,
Peter Milne,
Nidia Morrell,
S. E. Persson,
Miguel Roth,
Mathew Smith,
Nicholas B. Suntzeff
[show abstract]
[hide abstract]
ABSTRACT: A detailed study spanning approximately a year has been conducted on the Type
Ib supernova 2007Y. Imaging was obtained from X-ray to radio wavelengths, and a
comprehensive set of multi-band (w2m2w1u'g'r'i'UBVYJHKs) light curves and
optical spectroscopy is presented. A virtually complete bolometric light curve
is derived, from which we infer a (56)Ni-mass of 0.06 M_sun. The early spectrum
strongly resembles SN 2005bf and exhibits high-velocity features of CaII and
H_alpha; during late epochs the spectrum shows evidence of a ejecta-wind
interaction. Nebular emission lines have similar widths and exhibit profiles
that indicate a lack of major asymmetry in the ejecta. Late phase spectra are
modeled with a non-LTE code, from which we find (56)Ni, O and total-ejecta
masses (excluding He) to be 0.06, 0.2 and 0.42 M_sun, respectively, below 4,500
km/s. The (56)Ni mass confirms results obtained from the bolometric light
curve. The oxygen abundance suggests the progenitor was most likely a ~3.3
M_sun He core star that evolved from a zero-age-main-sequence mass of 10-13
M_sun. The explosion energy is determined to be ~10^50 erg, and the mass-loss
rate of the progenitor is constrained from X-ray and radio observations to be
<~10^-6 M_sun/yr. SN 2007Y is among the least energetic normal Type Ib
supernovae ever studied.
02/2009;
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[show abstract]
[hide abstract]
ABSTRACT: We present mid-infrared Period-Luminosity relations for Cepheids in the Local
Group galaxy IC1613. Using archival IRAC imaging data from Spitzer we were able
to measure single-epoch magnitudes for five, 7 to 50-day, Cepheids at 3.6 and
4.5 microns. When fit to the calibrating relations, measured for the Large
Magellanic Cloud Cepheids, the data give apparent distance moduli of 24.29 +/-
0.07 and 24.28 +/- 0.07 at 3.6 and 4.5 microns, respectively. A
multi-wavelength fit to previously published BVRIJHK apparent moduli and the
two IRAC moduli gives a true distance modulus of 24.27 +/- 0.02 mag with E(B-V)
= 0.08 mag, and a corresponding metric distance of 715 kpc. Given that these
results are based on single-phase observations derived from exposures having
total integration times of only 1,000 sec/pixel we suggest that Cepheids out to
about 2 Mpc are accessible to Spitzer with modest integration times during its
warm mission. We identify the main limiting factor to this method to be
crowding/contamination induced by the ubiquitous population of infrared-bright
AGB stars.
01/2009;
