Droit de réponse

Michard, Claire

doi:10.3406/jda.1992.1732

Cited by 7 publications

(9 citation statements)

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“…This correlation has been investigated here, taking determinations of core/power law and values of γ and a (4)/ a from the work of Pellegrini (1999), Rest et al (2001), Ravindranath, Ho & Filippenko (2002), Michard (1998), Faber et al (1997) and Bender et al (1989). For galaxies appearing in more than one paper, preference was in the order of the papers as listed, with the following exceptions.…”

Section: Resultsmentioning

confidence: 99%

Correlations of near-infrared, optical and X-ray luminosity for early-type galaxies

Ellis¹,

O’Sullivan²

2006

Monthly Notices of the Royal Astronomical Society

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The relation between X‐ray luminosity and near‐infrared (NIR) luminosity for early‐type galaxies has been examined. NIR luminosities should provide a superior measure of stellar mass compared to optical luminosities used in previous studies, especially if there is significant star formation or dust present in the galaxies. However, we show that the X‐ray–NIR relations are remarkably consistent with the X‐ray–optical relations. This indicates that the large scatter of the relations is dominated by scatter in the X‐ray properties of early‐type galaxies, and is consistent with early‐types consisting of old, quiescent stellar populations. We have investigated scatter in terms of environment, surface brightness profile, Mg2, Hβ, Hγ line strength indices, spectroscopic age and nuclear Hα emission. We found that galaxies with high Mg2 index, low Hβ and Hγ indices or a ‘core’ profile have a large scatter in LX, whereas galaxies with low Mg2, high Hβ and Hγ indices or ‘power‐law’ profiles generally have LX < 1041 erg s−1. There is no clear trend in the scatter with environment or nuclear Hα emission.

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Section: Resultsmentioning

confidence: 99%

Correlations of near-infrared, optical and X-ray luminosity for early-type galaxies

Ellis¹,

O’Sullivan²

2006

Monthly Notices of the Royal Astronomical Society

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“…All three galaxies have optical surface brightness profiles that are sharply peaked in the core (Michard 1998). It has been suggested that this type of profile is associated with discy, rapidly rotating galaxies (Nieto, Bender & Surma 1991) with low X‐ray and radio luminosities (Bender et al 1989).…”

Section: Discussionmentioning

confidence: 99%

XMM-NewtonandChandraobservations of three X-ray-faint early-type galaxies

O’Sullivan

Ponman

2004

Monthly Notices of the Royal Astronomical Society

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We present XMM–Newton observations of three X‐ray‐underluminous elliptical galaxies, NGC 3585, 4494 and 5322. All three galaxies have relatively large optical luminosities (log LB= 10.35–10.67 L⊙) but have X‐ray luminosities consistent with emission from discrete sources only. In conjunction with a Chandra observation of NGC 3585, we analyse the XMM–Newton data and show that the three galaxies are dominated by discrete source emission, but do possess some X‐ray‐emitting gas. The gas is at relatively low temperatures, kT≃ 0.25–0.44 keV. All three galaxies show evidence of recent dynamical disturbance and formation through mergers, including kinematically distinct cores, young stellar ages and embedded stellar discs. This leads us to conclude that the galaxies formed relatively recently and have yet to build up large X‐ray haloes. They are likely to be in a developmental phase where the X‐ray gas has a very low density, making it undetectable outside the galaxy core. However, if the gas is a product of stellar mass loss, as seems most probable, we would expect to observe supersolar metal abundances. While abundance is not well constrained by the data, we find best‐fitting abundances <0.1 Z⊙ for single‐temperature models, and it seems unlikely that we could underestimate the metallicity by such a large factor.

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“…Although the mean offset between the two scales is only 0.02 mag for 11.5 ≤ B t < 14.5, it is worth noting that the mutual scatter of 0.23 mag is considerably larger than the scatter of 0.04 mag found in Paper I (Young 2001) between a subset of 12 of the galaxies depicted in Fig. 1 and the magnitudes of Michard (1982). The main reason for this difference must be that whilst Michard (1982) used the same set of RC2 standard growth curves as used to derive the ERC2 magnitudes, for each galaxy he applied the best‐fitting RC2 growth curve rather than the one listed in the RC2 as appropriate to the type of the galaxy.…”

Section: Discussionmentioning

confidence: 55%

“…1 and the magnitudes of Michard (1982). The main reason for this difference must be that whilst Michard (1982) used the same set of RC2 standard growth curves as used to derive the ERC2 magnitudes, for each galaxy he applied the best‐fitting RC2 growth curve rather than the one listed in the RC2 as appropriate to the type of the galaxy. That there must have been some problems with the morphological‐type allocations of the RC2 growth curves even over the intermediate magnitude range is confirmed by the very much improved agreement between the RC3 B T and B t scales shown in Fig.…”

Section: Discussionmentioning

confidence: 99%

“…When, for any galaxy light profile, one instead adopts the best‐fitting curve from a comprehensive set of functions [whether this be the r n law, the linear interpolation between an r n <0.25 law and the r 1.00 law used by Prugniel & Héraudeau (1998), or even the RC2 or RC3 sets of growth curves cf. Michard (1982)]; one can reduce one's errors considerably. Consequently, the magnitude scale of Prugniel & Héraudeau (1998) offers a very major improvement on that of the RC3 not only in terms of scale errors but also in terms of random ones.…”

Section: Discussionmentioning

confidence: 99%

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Total magnitudes of Virgo galaxies - III. Scale errors in the Reference Catalogue of Bright Galaxies T system and light-profile distortion by resolution-degrading and differential-distance effects

Young¹

2004

Monthly Notices of the Royal Astronomical Society

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We investigate the BT magnitude scales of the Second and Third Reference Catalogues of Bright Galaxies, finding both scales to be reasonably reliable for 11.5 ≲Bt≲ 14.0. However, large‐scale errors of 0.26 and 0.24 mag per unit mag interval respectively are uncovered for early‐type galaxies at the bright ends, whilst even larger ones of 0.74 and 0.36 mag per unit mag interval are found for galaxies of all morphological types at the faint ends. We attribute this situation to several effects already discussed by Young et al. and Young (Paper I), including the application of relatively inflexible growth‐curve models that are only in a few specific cases appropriate to the galaxies concerned. Of particular interest to this study though, we find that the apparent profile shapes of giant galaxies in the Virgo direction of cz < 15 000 km s‐1 tend to be less centrally concentrated the greater their distance. This demonstrates that even for relatively nearby galaxies, the distortion of the overall shapes of light profiles by resolution‐degrading effects such as seeing and data smoothing, as originally predicted and modelled by Young & Currie and Young et al., is a significant effect. It is, therefore, not good practice simply to extrapolate the profiles of galaxies of identical intrinsic size and intrinsic profile shape (i.e. identical morphology) by means of the same growth‐curve model, unless the galaxies are known a priori to be at the same distance and unless their photometry is of the same angular resolution. We also investigate the total‐magnitude scale of the catalogue of photometric types of Prugniel & Héraudeau, finding it to be much more reliable than the BT one. However, we argue that photometric type is really a measure of apparent profile shape (i.e. intrinsic profile shape after scale reduction on account of distance followed by convolution with a seeing disc and often a smoothing function as well). Strictly, it should therefore only be applicable to comparisons between galaxies that are already known to be at similar distances provided that their photometry is also of similar angular resolution. Clearly, this must complicate attempts to construct quantitative morphological classification schemes for galaxies.

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Droit de réponse

Cited by 7 publications

References 0 publications

Correlations of near-infrared, optical and X-ray luminosity for early-type galaxies

Correlations of near-infrared, optical and X-ray luminosity for early-type galaxies

XMM-NewtonandChandraobservations of three X-ray-faint early-type galaxies

Total magnitudes of Virgo galaxies - III. Scale errors in the Reference Catalogue of Bright Galaxies T system and light-profile distortion by resolution-degrading and differential-distance effects

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