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Post Info TOPIC: Fornax A
Blobrana


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Posts: 131433
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NGC 1316
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Title: The distance to NGC1316 (Fornax A): yet another curious case
Authors: Michele Cantiello (1), Aniello Grado (2), John P. Blakeslee (3), Gianluca Di Rico (1), Luca Limatola (2), Enzo Brocato (1 and 4), Massimo Della Valle (2), Roberto Gilmozzi (5) ((1) INAF Osservatorio Astronomico di Teramo, (2) INAF Osservatorio Astronomico di Capodimonte, (3) Dominion Astrophysical Observatory, Herzberg Institute of Astrophysics, (4) INAF Osservatorio Astronomico di Roma, (5) European Southern Observatory)

The distance of NGC1316, the brightest galaxy in Fornax, is an interesting test for the cosmological distance scale. First, because Fornax is the 2nd largest cluster of galaxies at <~25 Mpc after Virgo and, in contrast to Virgo, has a small line-of-sight depth; and second, because NGC1316 is the galaxy with the largest number of detected SNeIa, giving the opportunity to test the consistency of SNeIa distances internally and against other indicators. 
We measure SBF mags in NGC1316 from ground and space-based imaging data, providing a homogeneous set of measurements over a wide wavelength interval. The SBF, coupled with empirical and theoretical calibrations, are used to estimate the distance to the galaxy. We present the first B-band SBF measurements of NGC1316 and use them together with the optical and near-IR SBF data to analyse the properties of field stars. 
Our distance modulus m-M=31.59 ±0.05(stat) ±0.14(sys), when placed in a consistent Cepheid distance scale, agrees with the results from other indicators. However, our result is ~17% larger than the most recent estimate based on SNeIa. Possible explanations for this disagreement are the uncertainties on internal extinction, or calibration issues. Concerning the stellar population analysis, we confirm earlier results from other indicators: the field stars in NGC1316 are dominated by a solar metallicity, intermediate age component. A substantial mismatch exists between B-band SBF models and data, a behaviour that can be accounted for by an enhanced percentage of hot horizontal branch stars. 
Our study of the SBF distance to NGC1316, and the comparison with distances from other indicators, raises some concern about the homogeneity between the calibrations of different indicators. If not properly placed in the same reference scale, significant differences can occur, with dramatic impact on the cosmological distance ladder.

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Blobrana


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Posts: 131433
Date:
SH2
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Title: The globular cluster system of NGC 1316. II - The extraordinary object SH2
Authors: T. Richtler, B. Kumar, L. P. Bassino, B. Dirsch, A. J. Romanowsky

SH2 has been described as an isolated HII-region, located about 6.5 arcmin south of the nucleus of NGC 1316 (Fornax A), a merger remnant in the the outskirts of the Fornax cluster of galaxies. We give a first, preliminary description of the stellar content and environment of this remarkable object. We used photometric data in the Washington system and HST photometry from the Hubble Legacy Archive for a morphological description and preliminary aperture photometry. Low-resolution spectroscopy provides radial velocities of the brightest star cluster in SH2 and a nearby intermediate-age cluster. SH2 is not a normal HII-region, ionised by very young stars. It contains a multitude of star clusters with ages of approximately 0.1 Gyr. A ring-like morphology is striking. SH2 seems to be connected to an intermediate-age massive globular cluster with a similar radial velocity, which itself is the main object of a group of fainter clusters. Metallicity estimates from emission lines remain ambiguous. The present data do not yet allow firm conclusions about the nature or origin of SH2. It might be a dwarf galaxy that has experienced a burst of extremely clustered star formation. We may witness how globular clusters are donated to a parent galaxy.

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Blobrana


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Posts: 131433
Date:
Fornax A
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Title: The globular cluster system of NGC1316. I. Wide-field photometry in the Washington system
Authors: T. Richtler, L. P. Bassino, B. Dirsch, B. Kumar

NGC 1316 (Fornax A) is a prominent merger remnant in the outskirts of the Fornax cluster. The cluster system has not yet been studied in its entirety. We therefore present a wide-field study of the globular cluster system of NGC 1316, investigating its properties in relation to the global morphology of NGC 1316. We used the MOSAIC II camera at the 4-m Blanco telescope at CTIO in the filters Washington C and Harris R. We identify globular cluster candidates and study their colour distribution and the structural properties of the system. In an appendix, we also make morphological remarks, present colour maps, and present new models for the brightness and colour profiles of the galaxy. The cluster system is well confined to the optically visible outer contours of NGC 1316. The colour distribution of the entire sample is unimodal, but the colour distribution of bright subsamples in the bulge shows two peaks that, by comparison with theoretical Washington colours with solar metallicity, correspond to ages of about 2 Gyr and 0.8 Gyr, respectively. We also find a significant population of clusters in the colour range 0.8 < C-R < 1.1 which must be populated by clusters younger than 0.8 Gyr, unless they are very metal-poor. The colour interval 1.3 < C-R < 1.6 hosts the bulk of intermediate-age clusters which show a surface density profile with a sharp decline at about 4 arcmin. The outer cluster population shows an unimodal colour distribution with a peak at C-R=1.1, indicating a larger contribution of old, metal-poor clusters. Their luminosity function does not show the expected turn-over, so the fraction of younger clusters is still significant. Cluster formation in NGC 1316 has continued after an initial burst, presumably related to the main merger. A toy model with two bursts of ages 2 Gyr and 0.8 Gyr is consistent with photometric properties and dynamical M/L-values.

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Blobrana


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Posts: 131433
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RE: NGC1316
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Title: Sizes, Half-Mass Densities, and Mass Functions of Star Clusters in the Merger Remnant NGC 1316: Clues to the Fate of Second-Generation Globular Clusters
Authors: Paul Goudfrooij (STScI)

We study mass functions of globular clusters derived from HST/ACS images of the early-type merger remnant galaxy NGC 1316 which hosts a significant population of metal-rich globular clusters of intermediate age (~3 Gyr). For the old, metal-poor (`blue') clusters, the peak mass of the mass function M_p increases with internal half-mass density rho_h as (M_p proportional to rho_h^0.44) whereas it stays approximately constant with galactocentric distance R_gal. The mass functions of these clusters are consistent with a simple scenario in which they formed with a Schechter initial mass function and evolved subsequently by internal two-body relaxation. For the intermediate-age population of metal-rich ("red") clusters, the faint end of the previously reported power-law luminosity function of the clusters with R_gal > 9 kpc is due to many of those clusters having radii larger than the theoretical maximum value imposed by the tidal field of NGC 1316 at their R_gal. This renders disruption by two-body relaxation ineffective. Only a few such diffuse clusters are found in the inner regions of NGC 1316. Completeness tests indicate that this is a physical effect. Using comparisons with star clusters in other galaxies and cluster disruption calculations using published models, we hypothesize that most red clusters in the low-rho_h tail of the initial distribution have already been destroyed in the inner regions of NGC 1316 by tidal shocking, and that several remaining low-rho_h clusters will evolve dynamically to become similar to "faint fuzzies" that exist in several lenticular galaxies. Finally, we discuss the nature of diffuse red clusters in early-type galaxies.

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Blobrana


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Title: Planetary nebula kinematics in NGC 1316: a young Sombrero
Authors: Emily K. McNeil-Moylan, Kenneth C. Freeman, Magda Arnaboldi, Ortwin E. Gerhard

Aims. We present positions and velocities for 796 planetary nebulae (PNe) in the Fornax Brightest Cluster Galaxy NGC 1316 (Fornax A). The planetary nebulae and existing kinematics are used to explore the rotation of this merger remnant and constrain dynamical models.
Methods. Using FORS2 on the VLT, the PN velocities were measured using a counter-dispersed slitless-spectroscopy technique that produced the largest-to-date sample outside of the Local Group. Spherical, non-rotating, constant-anisotropy Jeans models were constrained by observations of the planetary nebulae and existing integrated light spectra.
Results. The two-dimensional velocity field indicates dynamically-important rotation that rises in the outer parts, possibly due to the outward transfer of angular momentum during the merger. The modelling indicates a high dark matter content, particularly in the outer parts, that is consistent with previous estimates from dynamical models, lensing and stellar population models.
Conclusions. The exceptionally large sample of PN velocities makes it possible to explore the kinematics of NGC 1316 in detail. Comparing the results to other early-type galaxies like NGC 1399 and NGC 4594 (M104, Sombrero), NGC 1316 represents a transition phase from a major-merger event to a bulge-dominated galaxy like NGC 4594.

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Blobrana


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Title: The Distance to NGC 1316 (Fornax A) From Observations of Four Type Ia Supernovae
Authors: Maximilian Stritzinger, Chris Burns, Mark Phillips, Gaston Folatelli, Kevin Krisciunas, Eric Persson, Luis Boldt, Abdo Campillay, Carlos Contreras, Wojtek Krzeminski, Francisco Salgado, Wendy Freedman, Mario Hamuy, Barry Madore, Miguel Roth, Nicholas Suntzeff

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, 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 supernova, and the distance to NGC 1316. From the three normal supernovae, 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 values that are mutually consistent to 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 supernovae 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 supernovae. Nevertheless, two of them (SN 2006dd and SN 2006mr) show strong NaID interstellar lines in the host galaxy system. The strength of this absorption is completely inconsistent with the small reddening values derived from the supernova 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 NaID lines in SN 2006dd appear to have weakened significantly some 100-150 days after explosion.

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Blobrana


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Posts: 131433
Date:
Fornax A
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Title: Dark mammoth trunks in the merging galaxy NGC 1316 and a mechanism of cosmic double helices
Authors: Per Carlqvist

NGC 1316 is a giant, elliptical galaxy containing a complex network of dark, dust features. The morphology of these features has been examined in some detail using a Hubble Space Telescope, Advanced Camera for Surveys image. It is found that most of the features are constituted of long filaments. There also exist a great number of dark structures protruding inwards from the filaments. Many of these structures are strikingly similar to elephant trunks in H II regions in the Milky Way Galaxy, although much larger. The structures, termed mammoth trunks, generally are filamentary and often have shapes resembling the letters V or Y. In some of the mammoth trunks the stem of the Y can be resolved into two or more filaments, many of which showing signs of being intertwined. A model of the mammoth trunks, related to a recent theory of elephant trunks, is proposed. Based on magnetized filaments, the model is capable of giving an account of the various shapes of the mammoth trunks observed, including the twined structures.

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Blobrana


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RE: NGC1316
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Title: A Search for the Progenitors of Two Type-Ia Supernovae in NGC 1316
Authors: Dan Maoz, Filippo Mannucci
(Version v2)

Recent evidence of a young progenitor population for many Type-Ia SNe (SNe-Ia) raises the possibility that evolved intermediate-mass progenitor stars may be detected in pre-explosion images. NGC 1316, a radio galaxy in the Fornax cluster, is a prolific producer of SNe-Ia, with four detected since 1980. We analyse Hubble Space Telescope (HST) pre-explosion images of the sites of two of the SNe-Ia that exploded in this galaxy, SN2006dd (a normal Type-Ia) and SN2006mr (likely a subluminous, 1991bg-like, SN-Ia). Astrometric positions are obtained from optical and near-IR ground-based images of the events. We find no candidate point sources at either location, and set upper limits on the flux in B, V, and I from any such progenitors. We also estimate the amount of extinction that could be present, based on analysis of the surface-brightness inhomogeneities in the HST images themselves. At the distance of NGC 1316, the limits correspond to absolute magnitudes of about -5.5, -5.4, and -6.0 mag in M_B, M_V, and M_I, respectively. Comparison to stellar evolution models argues against the presence at the SN sites, 3 years prior to the explosion, of normal stars with initial masses > 6 M_sun at the tip of their asymptotic-giant branch (AGB) evolution, young post-AGB stars that had initial masses > 4 M_sun, and post-red-giant stars of initial masses > 9 M_sun.

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Blobrana


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Posts: 131433
Date:
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Title: A Search for the Progenitors of Two Type-Ia Supernovae in NGC 1316
Authors: Dan Maoz, Filippo Mannucci

Recent evidence of a young progenitor population for many Type-Ia SNe (SNe-Ia) raises the possibility that evolved intermediate-mass progenitor stars may be detected in pre-explosion images. NGC 1316, a radio galaxy in the Fornax cluster, is a prolific producer of SNe-Ia, with four detected since 1980. We analyse Hubble Space Telescope (HST) pre-explosion images of the sites of two of the SNe-Ia that exploded in this galaxy, SN2006dd (a normal Type-Ia) and SN2006mr (likely a subluminous, 1991bg-like, SN-Ia). Astrometric positions are obtained from optical and near-IR ground-based images of the events. We find no candidate point sources at either location, and set upper limits on the flux in B, V, and I from any such progenitors. We also estimate the amount of extinction that could be present, based on analysis of the surface-brightness inhomogeneities in the HST images themselves. At the distance of NGC 1316, the limits correspond to absolute magnitudes of about -5.5, -5.4, and -6.0 mag in M_B, M_V, and M_I, respectively. Comparison to stellar evolution models argues against the presence at the SN sites, 3 years prior to the explosion, of normal stars with initial masses > 4 M_sun at the tip of their asymptotic-giant branch (AGB) evolution, young post-AGB stars that had initial masses > 4 M_sun, and post-red-giant stars of initial masses > 9 M_sun.

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Blobrana


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Posts: 131433
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Scientists using NASA's Swift satellite stumbled upon a rare sight, two supernovas side by side in one galaxy. Large galaxies typically play host to three supernovas per century. Galaxy NGC 1316 has had two supernovas in less than five months, and a total of four supernova in 26 years, as far back as the records go. This makes NGC 1316 the most prodigious known producer of supernovas.

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