Surface Brightness Fluctuations Technique Research Articles

The Satellite Luminosity Function of M101 into the Ultra-faint Dwarf Galaxy Regime

Abstract We have obtained deep Hubble Space Telescope (HST) imaging of four faint and ultra-faint dwarf galaxy candidates in the vicinity of M101–Dw21, Dw22, Dw23 and Dw35, originally discovered by Bennet et al. Previous distance estimates using the surface brightness fluctuation technique have suggested that these four dwarf candidates are the only remaining viable M101 satellites identified in ground-based imaging out to the virial radius of M101 (D ≈ 250 kpc). Advanced Camera for Surveys imaging of all four dwarf candidates shows no associated resolved stellar populations, indicating that they are thus background galaxies. We confirm this by generating simulated HST color–magnitude diagrams of similar brightness dwarfs at the distance of M101. Our targets would have displayed clear, resolved red giant branches with dozens of stars if they had been associated with M101. With this information, we construct a satellite luminosity function for M101, which is 90% complete to M V = −7.7 mag and 50% complete to M V = −7.4 mag, that extends into the ultra-faint dwarf galaxy regime. The M101 system is remarkably poor in satellites in comparison to the Milky Way and M31, with only eight satellites down to an absolute magnitude of M V = −7.7 mag, compared to the 14 and 26 seen in the Milky Way and M31, respectively. Further observations of Milky Way analogs are needed to understand the halo-to-halo scatter in their faint satellite systems, and connect them with expectations from cosmological simulations.

A Precise Distance to the Host Galaxy of the Binary Neutron Star Merger GW170817 Using Surface Brightness Fluctuations∗

Abstract The joint detection of gravitational waves (GWs) and electromagnetic radiation from the binary neutron star (BNS) merger GW170817 has provided unprecedented insight into a wide range of physical processes: heavy element synthesis via the r-process; the production of relativistic ejecta; the equation of state of neutron stars and the nature of the merger remnant; the binary coalescence timescale; and a measurement of the Hubble constant via the “standard siren” technique. In detail, all of these results depend on the distance to the host galaxy of the merger event, NGC 4993. In this Letter we measure the surface brightness fluctuation (SBF) distance to NGC 4993 in the F110W and F160W passbands of the Wide Field Camera 3 Infrared Channel (WFC3/IR) on the Hubble Space Telescope (HST). For the preferred F110W passband we derive a distance modulus of ( m − M ) = 33.05 ± 0.08 ± 0.10 mag, or a linear distance d = 40.7 ± 1.4 ± 1.9 Mpc (random and systematic errors, respectively); a virtually identical result is obtained from the F160W data. This is the most precise distance to NGC 4993 available to date. Combining our distance measurement with the corrected recession velocity of NGC 4993 implies a Hubble constant H 0 = 71.9 ± 7.1 km s−1 Mpc−1. A comparison of our result to the GW-inferred value of H 0 indicates a binary orbital inclination of i ≳ 137°. The SBF technique can be applied to early-type host galaxies of BNS mergers to ∼100 Mpc with HST and possibly as far as ∼300 Mpc with the James Webb Space Telescope, thereby helping to break the inherent distance-inclination degeneracy of the GW data at distances where many future BNS mergers are likely to be detected.

Distances and stellar population properties for 12 elliptical galaxies

Aims. We use the surface brightness fluctuation (SBF) technique to derive the distances and analyse the radial behaviour of stellar populations in a sample of 12 elliptical galaxies. The data are I-band images collected with the FORS1 camera at the Very Large Telescope (VLT), drawn from the ESO archive. The main purpose of our analysis is to carry out the study of SBF magnitudes without relying on additional colour information that is normally required in SBF studies. Methods. We measure I-band SBF magnitudes and SBF variations with galaxy radii, which is useful for stellar population studies. Unlike typical applications of the SBF technique, the absolute SBF magnitudes needed to evaluate the distance moduli are derived using the fluctuation star count, ¯ N. Results. The distances obtained using the ¯ N calibration taken from the literature show a good agreement with available estimates. We find a median ∼0.2 mag difference between our and literature distance moduli, with the only exception of NGC 5090, which shows the I-band SBF ∼1 mag brighter than expected. The median statistical and systematic errors are ∼0.2 and ∼0.1 mag, respectively. On these grounds we consider the test of deriving SBF distances based on the ¯ N calibration to be successful. Taking into account that some of the previously estimated distances were made as long as 15 years ago, the new measurements provide an updated sketch on distances for a set of galaxies towards the region of the Great Attractor. Furthermore, gauging the SBF of the unresolved stellar systems has returned negative SBF radial gradients in the inner regions of five galaxies: a feature already known and explained by lower metallicity at larger galactic radii. Somehow unexpectedly, though, we detect positive SBF gradients at large radii (>20 kpc) in nine targets. This behaviour, if it is not caused by some unaccounted observational bias, could be explained at least partly as a statistical effect on the stellar counts at these radii. Additional (near-IR) observations are necessary to confirm the real existence of this feature and to allow us to reach more robust conclusions.

Tracing stellar populations of galaxies with the SBF method

Surface Brightness Fluctuations (SBF) are an useful distance indicator of gas-free galaxies as far as 100-150 Mpc with an accuracy of 5–10%. Recent applications have proved that the SBF technique is also a powerful tool to analyze the stellar content of elliptical-like galaxies by means of data/models comparison. Here we present a comprehensive study of the method on the base of a careful analysis of SBF models and a set of accurate multibands SBF measures obtained with HST.

HiDetection of Two Dwarf S0 Galaxies in Nearby Groups: ESO 384-016 and NGC 59

A H I survey of 10 dE/dS0 galaxies in the nearby Sculptor and Centaurus A groups was made using the Australia Telescope Compact Array. The observed galaxies have accurate distances derived by Jerjen et al. using the surface brightness fluctuation technique. Their absolute magnitudes are in the range -9.5 > MB > -15.3. Only two of the 10 galaxies were detected at our detection limit (~1.0 × 106 M⊙ for the Centaurus group and ~5.3 × 105 M⊙ for the Sculptor group): the two dS0 galaxies ESO 384-016 in the Centaurus A group and NGC 59 in the Sculptor group, with H I masses of × 106 and × 107 M⊙, respectively. Those two detections were confirmed using the Green Bank Telescope. These small H I reservoirs could fuel future generations of low-level star formation and could explain the bluer colors seen at the center of the detected galaxies. Similar to what is seen with the Virgo dwarf ellipticalss, the two objects with H I appear to be on the outskirts of the groups.

The ACS Virgo Cluster Survey. IV. Data Reduction Procedures for Surface Brightness Fluctuation Measurements with the Advanced Camera for Surveys

The Advanced Camera for Surveys (ACS) Virgo Cluster Survey is a large program to image 100 early-type Virgo galaxies using the F475W and F850LP bandpasses of the Wide Field Channel of the ACS instrument on the Hubble Space Telescope (HST). The scientific goals of this survey include an exploration of the three-dimensional structure of the Virgo Cluster and a critical examination of the usefulness of the globular cluster luminosity function as a distance indicator. Both of these issues require accurate distances for the full sample of 100 program galaxies. In this paper, we describe our data reduction procedures and examine the feasibility of accurate distance measurements using the method of surface brightness fluctuations (SBF) applied to the ACS Virgo Cluster Survey F850LP imaging. The ACS exhibits significant geometrical distortions owing to its off-axis location in the HST focal plane; correcting for these distortions by resampling the pixel values onto an undistorted frame results in pixel correlations that depend on the nature of the interpolation kernel used for the resampling. This poses a major challenge for the SBF technique, which normally assumes a flat power spectrum for the noise. We investigate a number of different interpolation kernels and show through an analysis of simulated galaxy images having realistic noise properties that it is possible, depending on the kernel, to measure SBF distances using distortion-corrected ACS images without introducing significant additional error from the resampling. We conclude by showing examples of real image power spectra from our survey.

New Optical and Near-Infrared Surface Brightness Fluctuation Models: A Primary Distance Indicator Ranging from Globular Clusters to Distant Galaxies?

We present new theoretical models for surface brightness fluctuations (SBFs) both for optical and near-infrared bands in standard ground-based and Hubble Space Telescope filter systems. Simple stellar population simulations are adopted. Models cover the age and metallicity ranges from 5 to 15 Gyr and from Z = 0.0001 to Z = 0.04, respectively. Effects due to variation of the initial mass function and the stellar color-temperature relation are explored. Particular attention is devoted to very bright stars in the color-magnitude diagram and to investigating the effects of mass loss along the red giant branch (RGB) and the asymptotic giant branch (AGB). It is found that U- and B-band SBF amplitudes are powerful diagnostics for the morphology of the horizontal branch and the post-AGB star population. We point out that a careful treatment of the mass-loss process along the RGB and AGB is fundamental to determining reliable SBF evaluations. The SBF measurements are used to place robust constraints on the evolution of AGB stars, suggesting that the mass-loss activity of AGB stars should be twice as efficient as that of RGB stars. Our models are able to reproduce the absolute SBF magnitudes of Galactic globular clusters and of galaxies and their integrated colors. New calibrations of absolute SBF magnitude in V, R, I, and K photometric filters are provided, which appear reliable enough to directly gauge distances, bypassing other distance indicators. The SBF technique is also used as a stellar population tracer to derive the age and metallicity of a selected sample of galaxies of known distances. Finally, SBF color versus integrated color diagrams are proposed as particularly useful in removing the well-known age-metallicity degeneracy affecting our knowledge of remote stellar systems.

Tip of the red giant branch distance for the Sculptor group dwarf ESO 540-032

We present the rst VICCD photometry for the Sculptor group galaxy ESO 540-032 obtained at the Very Large Telescope UT1+FORS1. The (I; V I) colour-magnitude diagram indicates that this intermediate- type dwarf galaxy is dominated by old, metal-poor ((Fe=H) 1:7 dex) stars, with a small population of slightly more metal-rich ((Fe=H) 1:3 dex), young (age 150 500 Myr) stars. A discontinuity in the I-band luminosity function is detected at I0 =2 3:44 0:09 mag. Interpreting this feature as the tip of the red giant branch and adopting MI = 4:20 0:10 mag for its absolute magnitude, we have determined a Population II distance modulus of (m M)0 =2 7:64 0:14 mag (3:4 0:2 Mpc). This distance conrms ESO 540-032 as a member of the nearby Sculptor group but is signicantly larger than a previously reported value based on the Surface Brightness Fluctuation (SBF) method. The results from stellar population synthesis models suggest that the application of the SBF technique on dwarf galaxies with mixed morphology requires a detailed knowledge of the underlying stellar composition and thus oers no advantage over a direct distance measurement using the tip of the red giant branch as distance indicator. We produce the surface brightness proles for ESO 540-032 and derive the photometric and structural parameters. The global properties follow closely the relations between metallicity and both absolute magnitude and central surface brightness dened by dwarf elliptical galaxies in the Local Group. Finally, we identify and discuss a non-stellar object near the galaxy center which may resemble a globular cluster.

Detection of Surface Brightness Fluctuations in NGC 4373 Using theHubble Space Telescope

Surface brightness fluctuations (SBF) have been detected for three elliptical galaxies-NGC 3379 in the Leo group, NGC 4406 in the Virgo cluster, and NGC 4373 in the Hydra-Centaurus supercluster-using marginally sampled, deep images taken with the Planetary Camera of the WFPC2 instrument on the Hubble Space Telescope (HST). The power spectrum of the fluctuations image is well fitted by an empirical model of the point-spread function constructed using point sources identified in the held. Comparison with high-quality ground-based observations of all three galaxies show excellent agreement in the measurement of the distance modulus over a substantial range in distance. This demonstrates the capability of the Planetary Camera of WFPC2 to measure distances using the SBF technique despite the marginal sampling and small spatial coverage of the images. The residual variance due to unresolved sources in all three galaxies is only 2%-5% of the detected fluctuations signal, which confirms the advantage of HST imaging in minimizing the uncertainty of this SBF correction. Extensive consistency checks, including an independent SBF analysis using an alternate software package, suggest that our internal uncertainties are <0.02 mag. The fluctuations magnitude for NGC 4373 is /_(F814W) = 31.31±0.05 mag, corresponding to a distance modulus of (m-M)_0 = 32.99±0.11. This implies a peculiar velocity for this galaxy of 415±330 km s^(-1), which is smaller than derived from the D_n-σ relation.

Calibration of the Surface Brightness Fluctution Method for use with the Hubble Space Telescope.

This paper presents the calibration of the surface brightness fluctuation (SBF) technique for use with the Wide Field and Planetary Camera-2 (WFPC-2) on the Hubble Space Telescope (HST). The calibration has a color term and zeropoint significantly different from the Kron-Cousins I-band SBF technique developed for ground-based observations. It is a required first step for using SBF at the larger distances now made possible with HST. WFPC-2 observations of 16 nearby galaxies through the F555W and F814W filters were tied to the V and I photometry of the ground-based SBF Survey (Tonry et al. 1997 [apj, 475, 399]). The calibration of the photometry agrees with that of Holtzman et al. (1995, pasp, 107, 1065) to within a few percent. We used a composite WFPC-2 point spread function (PSF) to measure mbar, and we found that SBF measurements are relatively insensitive to small variations in the PSF. The identification of globular clusters and dust is much easier with HST's high spatial resolution. We computed Mf8bar for the sample from the measured f8bar and the ground-based SBF Survey distance modulus. The best fitting calibration has Mf8bar = (-1.73 +/- 0.07) + (6.5 +/- 0.7) [viz - 1.15]. This color dependence is significantly steeper than the one for I_KC used on the ground. The total rms about this fit is 0.16 mag, reflecting not only the error in WFPC-2 measurements presented here but also the errors in the ground-based distance moduli. After accounting for additional sources of error of ~ 0.05-0.10 mag, the HST observations and ground-based observations are seen to contribute roughly equally to the residual error. We measured f8bar for NGC 3379 from the ground to check this calibration. The distance obtained using the F814W filter and the HST calibration agreed well with that obtained in the SBF Survey. For NGC 3379 we also compared the difference in fluctuation magnitudes Delta mbar between the I_KC and I_F814W filters to theoretical predictions for a typical old, metal rich population of a giant elliptical galaxy and found excellent agreement.

Detection of the Tip of the Red Giant Branch in NGC 5128

We present a color-magnitude diagram of more than 10,000 stars in the halo of the galaxy NGC 5128 (Centaurus A), based on WFPC2 images through V-band and I-band filters. The position of the red giant branch (RGB) stars is compared with the loci of the red giant branch in six well-studied globular clusters and in the dwarf elliptical galaxy NGC 185; the tip of the RGB is signalled by an observed turn-up in the luminosity function at I≃24.1 ± 0.1 mag; this yields a distance modulus (m - M)_0 = 27.8 ± 0.2 for NGC 5128 (i.e., a distance of 3.6 ± 0.2 Mpc), in agreement with previous determinations based on the planetary nebulae luminosity function and on the surface brightness fluctuations technique. The presence of an intermediate-age stellar population (~5 Gyr) is suggested by the luminosity function of the asymptotic giant branch stars, extending up to I= 22.6 mag (for V - I > 2) and M_(bot) ~ -5 mag; however, the number of these stars constrains the intermediate-age stellar population in the halo of NGC 5128 to be less than ~ 10% of the total. The color distribution at constant I magnitude, albeit affected by the completeness level of our sample, strongly suggests a mean value of [Fe/H] > -0.9 dex, possibly similar to the value found in M31 and higher than that observed in NGC 185. Like the M31 halo, the halo of NGC 5128 exhibits a broad range of levels of chemical enrichment.