The puzzle about the radial cut-off in galactic disks

Narayan, Chaitra A.; Jog, Chanda J.

doi:10.1051/0004-6361:20031052

Cited by 12 publications

(13 citation statements)

References 27 publications

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“…Such truncated surface brightness profiles are in fact commonly observed among disc galaxies (for a recent review, see Pohlen et al 2004), and one might ask whether some fraction of these features may be due to EBL extinction effects rather than intrinsic disc truncations. The possibility that artificial disc truncations may arise from oversubtraction of sky has previously been discussed by Barteldrees & Dettmar (1994)de Grijs, Kregel & Wesson (2001) and Narayan & Jog (2003), but the effect discussed here is markedly different, since the amount of oversubtraction associated with the EBL is a function of both intrinsic disc surface brightness and dust content. Observationally, the truncation radius of both high and low‐surface‐brightness discs appears at an average I ‐band surface brightness of μ I ≈ 25.3 mag arcsec −2 (Kregel & van der Kruit 2004).…”

Section: Impact On Studies Of Disc Truncationsmentioning

confidence: 72%

How the extinction of extragalactic background light affects surface photometry of galaxies, groups and clusters

Zackrisson

Micheva

Östlin

2009

Monthly Notices of the Royal Astronomical Society

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The faint regions of galaxies, groups and clusters hold important clues about how these objects formed, and surface photometry at optical and near‐infrared wavelengths represents a powerful tool for studying such structures. Here, we identify a hitherto unrecognized problem with this technique, related to how the night sky flux is typically measured and subtracted from astronomical images. While most of the sky flux comes from regions between the observer and the target object, a small fraction – the extragalactic background light (EBL) – comes from behind. We argue that since this part of the sky flux can be subjected to extinction by dust present in the galaxy/group/cluster studied, standard reduction procedures may lead to a systematic oversubtraction of the EBL. Even very small amounts of extinction can lead to spurious features in radial surface brightness profiles and colour maps of extended objects. We assess the likely impact of this effect on a number of topics in extragalactic astronomy where very deep surface photometry is currently attempted, including studies of stellar haloes, starburst host galaxies, disc truncations and diffuse intragroup/intracluster light. We argue that EBL extinction may provide at least a partial explanation for the anomalously red colours reported for the haloes of disc galaxies and for the hosts of local starburst galaxies. EBL extinction effects also mimic truncations in discs with unusually high dust opacities, but are unlikely to be the cause of such features in general. Failure to account for EBL extinction can also give rise to a non‐negligible underestimate of intragroup and intracluster light at the faintest surface brightness levels currently probed. Finally, we discuss how EBL extinction effects may be exploited to provide an independent constraint on the surface brightness of the EBL, using a combination of surface photometry and direct star counts.

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Section: Impact On Studies Of Disc Truncationsmentioning

confidence: 72%

How the extinction of extragalactic background light affects surface photometry of galaxies, groups and clusters

Zackrisson

Micheva

Östlin

2009

Monthly Notices of the Royal Astronomical Society

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“…However, it is clear that truncations -seen in different data sets, using different methods, and analysed by different groups -are real, in contrast to the recent claim of Narayan & Jog (2003). It is not a matter of "questioning their very existence", but rather of determining the shape of the profiles beyond the break radius, which is admittedly still difficult to measure and a "puzzle" to explain.…”

Section: The Combined Viewmentioning

confidence: 97%

Stellar Disk Truncations: Where Do We Stand?

Pohlen

Beckman

Hüttemeister

et al. 2004

Astrophysics and Space Science Library

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In the light of several recent developments we revisit the phenomenon of galactic stellar disk truncations. Even 25 years since the first paper on outer breaks in the radial light profiles of spiral galaxies, their origin is still unclear. The two most promising explanations are that these 'outer edges' either trace the maximum angular momentum during the galaxy formation epoch, or are associated with global star formation thresholds. Depending on their true physical nature, these outer edges may represent an improved size characteristic (e.g., as compared to D25) and might contain fossil evidence imprinted by the galaxy formation and evolutionary history. We will address several observational aspects of disk truncations: their existence, not only in normal HSB galaxies, but also in LSB and even dwarf galaxies; their detailed shape, not sharp cut-offs as thought before, but in fact demarcating the start of a region with a steeper exponential distribution of starlight; their possible association with bars; as well as problems related to the line-of-sight integration for edge-on galaxies (the main targets for truncation searches so far). Taken together, these observations currently favour the star-formation threshold model, but more work is necessary to implement the truncations as adequate parameters characterising galactic disks.

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“…They proposed that lopsided features which were identified in 30 per cent of the galaxies by Zaritsky & Rix (1997) might produce such resonances. Some authors have suggested that broken exponentials may reflect variations in disc intensity due to clumpy SF, spiral arms or ring‐like features (Narayan & Jog 2003). Erwin, Pohlen & Beckman (2008) found that 42 per cent of a sample of 66 barred galaxies showed breaks.…”

Section: Background and Motivationmentioning

confidence: 99%

An N-body/SPH study of isolated galaxy mass density profiles

Foyle

Courteau

Thacker

2008

Monthly Notices RAS

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We investigate the evolution of mass density profiles in secular disc galaxy models, paying special attention to the development of a two‐component profile from a single initial exponential disc free of cosmological evolution (i.e. no accretion or interactions). As the source of density profile variations, we examine the parameter space of the spin parameter, halo concentration, virial mass, disc mass and bulge mass, for a total of 162 simulations in the context of a plausible model of star formation and feedback. The isolated galaxy models are based on the method of Springel & White and were evolved using the N‐body/SPH code gadget‐2. The initially pure exponential discs have a minimum of 1.4 million particles and most models were evolved over a period of 10 Gyr. We find that the slope of the outer density profile is in close agreement with that of the initial profile and remains stable over time, whereas the inner density profile slope evolves considerably as a result of angular momentum redistribution. The evolution of the galaxy mass density profile, including the development of a two‐component profile with an inner and outer segment, is controlled by the ratio of the disc mass fraction, md, to the halo spin parameter, λ. The location of the break between the two components and speed at which it develops is directly proportional to md/λ; the amplitude of the transition between the inner and outer regions is however controlled by the ratio of halo concentration to virial velocity. The location of the divide between the inner and outer profile does not change with time. The condition for a two‐component profile is roughly md/λ≥ 1. While the development of a two‐component density profile is coupled to bar formation, not all barred galaxies develop a two‐component profile. A galaxy model showing a clear minimum Toomre Q, normally linked to a double exponential in the stellar profile, may never exhibit any two‐component feature thus yielding a fully evolved pure exponential disc.

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The puzzle about the radial cut-off in galactic disks

Cited by 12 publications

References 27 publications

How the extinction of extragalactic background light affects surface photometry of galaxies, groups and clusters

How the extinction of extragalactic background light affects surface photometry of galaxies, groups and clusters

Stellar Disk Truncations: Where Do We Stand?

An N-body/SPH study of isolated galaxy mass density profiles

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