We present the first pointed X-ray observations of 10 candidate fossil galaxy groups and clusters. With these Suzaku observations, we determine global temperatures and bolometric X-ray luminosities ...of the intracluster medium (ICM) out to r
500 for six systems in our sample. The remaining four systems show signs of significant contamination from non-ICM sources. For the six objects with successfully determined r
500 properties, we measure global temperatures in the range 2.8 ≤ T
X ≤ 5.3 keV, bolometric X-ray luminosities of 0.8 × 1044 ≤ L
X, bol ≤ 7.7 × 1044 erg s−1, and estimate masses, as derived from T
X, of M
500 ≳ 1014 M⊙. Fossil cluster scaling relations are constructed for a sample that combines our Suzaku observed fossils with fossils in the literature. Using measurements of global X-ray luminosity, temperature, optical luminosity, and velocity dispersion, scaling relations for the fossil sample are then compared with a control sample of non-fossil systems. We find the fits of our fossil cluster scaling relations are consistent with the relations for normal groups and clusters, indicating fossil clusters have global ICM X-ray properties similar to those of comparable mass non-fossil systems.
ABSTRACT
We present a study on the star formation histories (SFHs) of galaxies covering the range 104 < M⋆/M⊙ < 1012, leveraging full spectral fitting algorithms. Our sample consists of 31 dwarf ...galaxies from the SAMI-Fornax Survey with stellar masses between 107–$10^{9.5} \, {\rm M}_{\odot }$, early-type galaxies from the ATLAS3D project with stellar masses between 1010–$10^{12} \, {\rm M}_{\odot }$, and dwarf galaxies that are satellites of Andromeda and the Milky Way, with 104 < M⋆/M⊙ < 108. We find that galaxies from 107–$10^{8} \, {\rm M}_{\odot }$ exhibit the smallest star formation rates (SFRs), while the SFR increase as we move down or up in mass. In this sense, we find that some $10^{5} \, {\rm M}_{\odot }$ galaxies have cumulative SFHs that are comparable to those of $10^{12} \, {\rm M}_{\odot }$ galaxies. Our study shows that the evolution of giant galaxies is primarily governed by their internal properties, with time-scales that do not depend on their environmental location. In contrast, dwarf galaxies below $10^{8} \, {\rm M}_{\odot }$ can be significantly affected in dense environments, such as the inner regions of a cluster, that severely quench the galaxies before the assembly of their 50 per cent present-day mass. We find that, only dwarfs with stellar masses between 107–$10^{9} \, {\rm M}_{\odot }$ actively form stars nowadays, while less massive galaxies seem to remain unaffected by the environment due to the expulsion of most of their gas at an early stage in their evolution. Our study highlights and corroborates a critical threshold around $10^{8}-10^{9} \, {\rm M}_{\odot }$ in galaxy evolution from previous studies, separating more massive galaxies minimally impacted by the environment from those less massive galaxies quenched by it.
Context. The tumbling pattern of a bar is the main parameter characterising its dynamics. From numerical simulations, its evolution since bar formation is tightly linked to the dark halo in which the ...bar is formed through dynamical friction and angular momentum exchange. Observational measurements of the bar pattern speed with redshift can restrict models of galaxy formation and bar evolution. Aims. We aim to determine for the first time the bar pattern speed evolution with redshift based on morphological measurements. Methods. We have selected a sample of 44 low-inclination ringed galaxies from the SDSS and COSMOS surveys covering the redshift range 0 < z < 0.8 to investigate the evolution of the bar pattern speed. We derived morphological ratios between the deprojected outer ring radius (Rring) and the bar size (Rbar). This quantity is related to the parameter ℛ = RCR/Rbar used for classifiying bars in slow and fast rotators, and allows us to investigate possible differences with redshift. Results. We obtain a similar distribution of R at all redshifts. We do not find any systematic effect that could be forcing this result. Conclusions. The results obtained here are compatible with the main bulk of the bar population (~70%) being fast-rotators and with no evolution of the pattern speed with redshift. We argue that if bars are long-lasting structures, the results presented here imply that there has not been a substantial angular momentum exchange between the bar and halo, as predicted by numerical simulations. In consequence, this might imply that the discs of these high surface-brightness galaxies are maximal.
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We consistently analyse for the first time the impact of survey depth and spatial resolution on the most used morphological parameters for classifying galaxies through non-parametric methods: Abraham ...and Conselice–Bershady concentration indices, Gini, M20 moment of light, asymmetry, and smoothness. Three different non-local data sets are used, Advanced Large Homogeneous Area Medium Band Redshift Astronomical (ALHAMBRA) and Subaru/XMM-Newton Deep Survey (SXDS, examples of deep ground-based surveys), and Cosmos Evolution Survey (COSMOS, deep space-based survey). We used a sample of 3000 local, visually classified galaxies, measuring their morphological parameters at their real redshifts (z ∼ 0). Then we simulated them to match the redshift and magnitude distributions of galaxies in the non-local surveys. The comparisons of the two sets allow us to put constraints on the use of each parameter for morphological classification and evaluate the effectiveness of the commonly used morphological diagnostic diagrams. All analysed parameters suffer from biases related to spatial resolution and depth, the impact of the former being much stronger. When including asymmetry and smoothness in classification diagrams, the noise effects must be taken into account carefully, especially for ground-based surveys. M20 is significantly affected, changing both the shape and range of its distribution at all brightness levels. We suggest that diagnostic diagrams based on 2–3 parameters should be avoided when classifying galaxies in ground-based surveys, independently of their brightness; for COSMOS they should be avoided for galaxies fainter than F814 = 23.0. These results can be applied directly to surveys similar to ALHAMBRA, SXDS and COSMOS, and also can serve as an upper/lower limit for shallower/deeper ones.
We present the results of high-resolution absorption-line spectroscopy of three face-on galaxies, NGC 98, NGC 600, and NGC 1703, with the aim of searching for box/peanut (B/P) shaped bulges. These ...observations test and confirm, for the first time, the prediction that face-on B/P-shaped bulges can be recognized by two minima in the profile along the bar's major axis of the fourth Gauss-Hermite moment h sub(4) of the line-of-sight velocity distribution (LOSVD). In NGC 98, a clear double minimum in h sub(4) is present along the major axis of the bar and before the end of the bar, as predicted. In contrast, in NGC 600, which is also a barred galaxy but lacks a substantial bulge, we do not find any significant kinematic signature for a B/P-shaped bulge. In NGC 1703, which is an unbarred control galaxy, we found no evidence of a B/P bulge. We also show directly that the LOSVD is broader at the location of the h sub(4) minimum in NGC 98 than elsewhere. This more direct method avoids possible artifacts associated with the degeneracy between the measurement of LOSVD and h sub(4).
We present the study of the colour–magnitude diagram of the cluster Abell 2151 (A 2151), with a particular focus on the low-mass end. The deep spectroscopy with AF2/WYFFOS@WHT and the caustic method ...enable us to obtain 360 members within 1.3 R
200 and absolute magnitude
$M_r \lesssim M_r^{\ast }+6$
. This nearby cluster shows a well defined red sequence up to M
r
∼ −18.5; at fainter magnitudes only 36 per cent of the galaxies lie on the extrapolation of the red sequence. We compare the red sequences of A 2151 and Abell 85, which is another nearby cluster with similar spectroscopic data, but with different mass and dynamical state. Both clusters show similar red sequences at the bright end (M
r
≤ −19.5), whereas large differences appear at the faint end. This result suggests that the reddening of bright galaxies is independent of environment, unlike the dwarf population (M
r
≥ −18.0).
We study the clustering of galaxies as function of luminosity and redshift in the range 0.35 < z < 1.25 using data from the Advanced Large Homogeneous Area Medium-Band Redshift Astronomical ...(ALHAMBRA) survey. The ALHAMBRA data used in this work cover 2.38 deg2 in seven independent fields, after applying a detailed angular selection mask, with accurate photometric redshifts, σ
z
≲ 0.014(1 + z), down to I
AB < 24. Given the depth of the survey, we select samples in B-band luminosity down to L
th ≃ 0.16L* at z = 0.9. We measure the real-space clustering using the projected correlation function, accounting for photometric redshifts uncertainties. We infer the galaxy bias, and study its evolution with luminosity. We study the effect of sample variance, and confirm earlier results that the Cosmic Evolution Survey (COSMOS) and European Large Area ISO Survey North 1 (ELAIS-N1) fields are dominated by the presence of large structures. For the intermediate and bright samples, L
med ≳ 0.6L*, we obtain a strong dependence of bias on luminosity, in agreement with previous results at similar redshift. We are able to extend this study to fainter luminosities, where we obtain an almost flat relation, similar to that observed at low redshift. Regarding the evolution of bias with redshift, our results suggest that the different galaxy populations studied reside in haloes covering a range in mass between log10M
h/( h
−1 M⊙) ≳ 11.5 for samples with L
med ≃ 0.3L* and log10M
h/( h
−1 M⊙) ≳ 13.0 for samples with L
med ≃ 2L*, with typical occupation numbers in the range of ∼1–3 galaxies per halo.
Context. Early-type dwarf (dE) galaxies are the most common type of galaxies observed in the Universe. Their study has important cosmological implications because according to hierarchical galaxy ...evolution theories they are the progenitors of brighter galaxies. Nevertheless, the origin of this kind of system is still not well understood. Aims. The aim of the present work is to investigate whether the different locations of dwarf galaxies with respect to ellipticals in the face-on view of the fundamental plane could be due to the transformation of bright disc galaxies in low-mass systems by harassment. Methods. We have run high-resolution N-body numerical simulations to test the tidal stripping scenario of dE galaxies. The present simulations modelled several individual tidal stripping events in initial disc-like galaxy models with different bulge-to-disc mass ratios. Results. The models have shown that tidal stripping is a very efficient mechanism for removing stars and dark matter particles from galaxies, specially from their outer parts. The particles of the disc and halo components were easily stripped, while the bulge particles were not. Thus, the scale length of the discs were 40-50% shorter than the initial ones. Prograde tidal interactions create tidal features like stable bars in the discs of the galaxies. In contrast, bars are inhibited in retrograde encounters. After several tidal interactions the galaxy remnants looks like a dwarf spheroidal system. The final position of the low-mass systems in the face-on view of the fundamental plane (FP) depends on the initial conditions of the simulations. Thus, simulated galaxies with initial large $B/D$ ratios are closer to the face-on view of the fundamental plane defined by bright E and bulges of early-type galaxies. Nevertheless, galaxies with initially small $B/D$ ratio are located, after four fast tidal encounters, at the position of dE galaxies in the face-on view of the fundamental plane.The final position of the remnants in the FP do not depend on the orbital configuration of the encounters. Conclusions. We conclude that fast galaxy-galaxy interactions are efficient mechanisms of transforming bright galaxies into dwarf ones. Indeed, the different location observed between Es and dEs in the face-on view of the fundamental plane can be explained by the formation of dwarf galaxies by harassment of late-type bright ones.
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