Blue E/S0 galaxies: merger remnants or disk rebuilding galaxies?
This paper has been withdrawn A new version is in preparation and will be soon available.
astro-ph.CO↗
arXiv subjects
J. A. L. Aguerri
Publications and source records attributed to J. A. L. Aguerri.
The influence of the environment on bar formation
Galaxy mergers and interactions are mechanisms which could drive the formation of bars. Therefore, we could expect that the fraction of barred galaxies increases with the local density. Here we show the first results of an extensive search for barred galaxies in different environments. We conclude that the bar fraction on bright (L>L*) field, Virgo, and Coma cluster galaxies is compatible. These results point towards an scenario where the formation and/or evolution of bars depend mostly on internal galaxy processes rather than external ones.
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The Host in Blue Compact Galaxies: Structural Properties and Scaling Relations
We have characterized the underlying stellar host in a sample of 28 blue compact galaxies (BCGs), by fitting their 2D light distributions. Their structural parameters were related with galaxy properties such as colours and gas content. These properties were also compared with those of other galaxy types. All the BCG hosts but one show low Sersic indexes (0.5 < n < 2), with mean effective radius <$r_{e,B}$>=1.11$\pm$0.74 kpc, and mean surface brightness <$μ_{e,B}$> = 22.59$\pm$0.68 mag arcsec$^{-2}$. Host effective radii scale linearly with their luminosity, while n and $μ_{\rm e}$ do not. In addition, host colours and structural parameters are not linearly correlated. Overall,the flux enhancement caused by the starburst is about 0.8 mag while their B-R colours decrease by about 0.2 mag. Galaxies with more luminous and extended hosts show larger and luminous starburst components. BCG hosts show B-R=0.95$\pm$0.26 in median. Overall, BCG hosts are more compact (by a factor ~2) and have higher central surface brightnesses (by about ~2 mag) than dIs and most dEs. BCG hosts and dIs are indistinguishable in the B-band Tully-Fisher relation (TFR). We found that about 50-60 % of the galaxies are more underluminous than those late-type discs with the same circular velocity. This feature is more important when luminosities are converted into stellar masses, while it tends to diminish when the HI gas mass is added. Deviations among host masses for a given circular velocity from the stellar TFR correlate with their HI mass-to-luminosity ratio, whereas deviations from the gas+stellar TFR, do not. Overall, our findings suggest that the baryonic mass in BCGs tends to normal values but BCGs tend to be inefficient producing stars, especially toward the low-mass, gas-rich and bluest hosts, in a similar way to dIs.
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Search for blue compact dwarf galaxies during quiescence II: metallicities of gas and stars, ages, and star-formation rates
We examine the metallicity and age of a large set of SDSS/DR6 galaxies that may be Blue Compact Dwarf (BCD) galaxies during quiescence (QBCDs).The individual spectra are first classified and then averaged to reduce noise. The metallicity inferred from emission lines (tracing ionized gas) exceeds by ~0.35 dex the metallicity inferred from absorption lines (tracing stars). Such a small difference is significant according to our error budget estimate. The same procedure was applied to a reference sample of BCDs, and in this case the two metallicities agree, being also consistent with the stellar metallicity in QBCDs. Chemical evolution models indicate that the gas metallicity of QBCDs is too high to be representative of the galaxy as a whole, but it can represent a small fraction of the galactic gas, self enriched by previous starbursts. The luminosity weighted stellar age of QBCDs spans the whole range between 1 and 10 Gyr, whereas it is always smaller than 1 Gyr for BCDs. Our stellar ages and metallicities rely on a single stellar population spectrum fitting procedure, which we have specifically developed for this work using the stellar library MILES.
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Near-IR Galaxy Counts and Evolution from the Wide-Field ALHAMBRA survey
The ALHAMBRA survey aims to cover 4 square degrees using a system of 20 contiguous, equal width, medium-band filters spanning the range 3500 A to 9700 A plus the standard JHKs filters. Here we analyze deep near-IR number counts of one of our fields (ALH08) for which we have a relatively large area (0.5 square degrees) and faint photometry (J=22.4, H=21.3 and K=20.0 at the 50% of recovery efficiency for point-like sources). We find that the logarithmic gradient of the galaxy counts undergoes a distinct change to a flatter slope in each band: from 0.44 at [17.0, 18.5] to 0.34 at [19.5, 22.0] for the J band; for the H band 0.46 at [15.5, 18.0] to 0.36 at [19.0, 21.0], and in Ks the change is from 0.53 in the range [15.0, 17.0] to 0.33 in the interval [18.0, 20.0]. These observations together with faint optical counts are used to constrain models that include density and luminosity evolution of the local type-dependent luminosity functions. Our models imply a decline in the space density of evolved early-type galaxies with increasing redshift, such that only 30% - 50% of the bulk of the present day red-ellipticals was already in place at z~1.
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The population of barred galaxies in the local universe I. Detection and characterisation of bars
(Abridge) Bars are very common in the centre of the disc galaxies, and they drive the evolution of their structure. A volume-limited sample of 2106 disc galaxies extracted from the Sloan Digital Sky Survey Data Release 5 was studied to derive the bar fraction, length, and strength as a function of the morphology, size, local galaxy density, light concentration, and colour of the host galaxy. The bars were detected using the ellipse fitting method and Fourier analysis method. The ellipse fitting method was found to be more efficient in detecting bars in spiral galaxies. The fraction of barred galaxies turned out to be 45%. A bar was found in 29% of the lenticular galaxies, in 55% and 54% of the early- and late-type spirals, respectively. The bar length (normalised by the galaxy size) of late-type spirals is shorter than in early-type or lenticular ones. A correlation between the bar length and galaxy size was found with longer bars hosted by larger galaxies. The bars of the lenticular galaxies are weaker than those in spirals. Moreover, the unimodal distribution of the bar strength found for all the galaxy types argues against a quick transition between the barred and unbarred statues. There is no difference between the local galaxy density of barred and unbarred galaxies. Besides, neither the length nor strength of the bars are correlated with the local density of the galaxy neighbourhoods. In contrast, a statistical significant difference between the central light concentration and colour of barred and unbarred galaxies was found. Bars are mostly located in less concentrated and bluer galaxies. These results indicate that the properties of bars are strongly related to those of their host galaxies, but do not depend on the local environment.
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Optimal filter systems for photometric redshift estimation
In the next years, several cosmological surveys will rely on imaging data to estimate the redshift of galaxies, using traditional filter systems with 4-5 optical broad bands; narrower filters improve the spectral resolution, but strongly reduce the total system throughput. We explore how photometric redshift performance depends on the number of filters n_f, characterizing the survey depth through the fraction of galaxies with unambiguous redshift estimates. For a combination of total exposure time and telescope imaging area of 270 hrs m^2, 4-5 filter systems perform significantly worse, both in completeness depth and precision, than systems with n_f >= 8 filters. Our results suggest that for low n_f, the color-redshift degeneracies overwhelm the improvements in photometric depth, and that even at higher n_f, the effective photometric redshift depth decreases much more slowly with filter width than naively expected from the reduction in S/N. Adding near-IR observations improves the performance of low n_f systems, but still the system which maximizes the photometric redshift completeness is formed by 9 filters with logarithmically increasing bandwidth (constant resolution) and half-band overlap, reaching ~0.7 mag deeper, with 10% better redshift precision, than 4-5 filter systems. A system with 20 constant-width, non-overlapping filters reaches only ~0.1 mag shallower than 4-5 filter systems, but has a precision almost 3 times better, dz = 0.014(1+z) vs. dz = 0.042(1+z). We briefly discuss a practical implementation of such a photometric system: the ALHAMBRA survey.
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On the Origin of Dwarf Elliptical Galaxies: The Fundamental Plane
Early-type dwarf galaxies are the most common type of galaxies observed in the Universe. The origin of this kind of systems is still not well understood. The aim of this paper 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. We have run high-resolution N-body numerical simulations to test the tidal stripping scenario of the dE galaxies. The present simulations modelled several individual tidal stripping events on initial disc-like galaxy models with different bulge-to-disc mass ratios. Tidal stripping is a very efficient mechanism for removing stars and dark matter particles from galaxies. The particles of the disc and halo components were easily stripped, while the bulge 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. After several tidal interactions the galaxy remnants looks like a dwarf spheroidal system. 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 initial 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. We conclude that fast galaxy-galaxy interactions are efficient mechanisms for transforming bright galaxies in 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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The ALHAMBRA Project: A large area multi medium-band optical and NIR photometric survey
(ABRIDGED) We describe the first results of the ALHAMBRA survey which provides cosmic tomography of the evolution of the contents of the Universe over most of Cosmic history. Our approach employs 20 contiguous, equal-width, medium-band filters covering from 3500 to 9700 A, plus the JHKs bands, to observe an area of 4 sqdeg on the sky. The optical photometric system has been designed to maximize the number of objects with accurate classification by SED and redshift, and to be sensitive to relatively faint emission lines. The observations are being carried out with the Calar Alto 3.5m telescope using the cameras LAICA and O-2000. The first data confirm that we are reaching the expected magnitude limits of AB<~25 mag in the optical filters from the blue to 8300 A, and from AB=24.7 to 23.4 for the redder ones. The limit in the NIR is (Vega) K_s~20, H~21, J~22. We expect to obtain accurate redshift values, Delta z/(1+z) <~ 0.03 for about 5x10^5 galaxies with I<~25 (60% complete), and z_med=0.74. This accuracy, together with the homogeneity of the selection function, will allow for the study of the redshift evolution of the large scale structure, the galaxy population and its evolution with redshift, the identification of clusters of galaxies, and many other studies, without the need for any further follow-up. It will also provide targets for detailed studies with 10m-class telescopes. Given its area, spectral coverage and its depth, apart from those main goals, the ALHAMBRA-Survey will also produce valuable data for galactic studies.
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The bright galaxy population of five medium redshift clusters. I. Color-Magnitude Relation, Blue Fractions and Visual Morphology
Using data of five clusters of galaxies within the redshift range 0.15 $\leq$ z $\leq$ 0.25, imaged with the Nordic Optical Telescope (NOT) in the central $\approx$ 1 Mpc$^2$ in very good seeing conditions, we have performed an exhaustive inspection of their bright galaxy population. That range of redshift, where only a small amount of data with the required resolution and quality is available, is particularly important for the understanding of the formation and evolution of clusters of galaxies. We have inspected the color-magnitude relation (CMR) for those clusters and measured the blue fraction of galaxies in their cores to check for evidence of evolution as found in other works. Moreover, the visual classification of the galaxy morphology has been performed and the morphology-radius relation has been examined We have not found signs of evolution neither in the slope of the CMR nor in the blue fraction of galaxies. A diversity of situations regarding those parameters and in the morphological mixing has been noticed, with two out of five clusters containing a dominant late-type core population. The cluster A1878 stands out as some of its properties differ from those of the other clusters in the sample. No clear signs of evolution appear in our analysis. The data support the view that the morphology and the stellar content of the galaxies in our clusters have been already settled at z $\sim$ 0.2. Only the fraction of interacting galaxies in the clusters appear to be larger than in clusters like Coma although the number of clusters in the sample is small to give a definitive conclusion.
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First results from the ALHAMBRA-Survey
We present the first results from the ALHAMBRA survey. ALHAMBRA will cover a relatively wide area (4 square degrees) using a purposely-designed set of 20 medium-band filters, down to an homogeneous magnitude limit AB~25 in most of them, adding also deep near-infrared imaging in JHK. To this aim we are using the Calar Alto 3.5m telescope. A small area of the ALHAMBRA survey has already been observed through our complete filter set, and this allows for the first time to check all the steps of the survey, including the pipelines that have been designed for the project, the fulfilment of the data quality expectations, the calibration procedures, and the photometric redshift machinery for which ALHAMBRA has been optimised. We present here the basic results regarding the properties of the galaxy sample selected in a 15x15 square arcmin area of the ALHAMBRA-8 field, which includes approximately 10000 galaxies with precise photometric redshift measurements. In a first estimate, approximately 500 of them must be galaxies with z>2.
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Confirmation of a Kinematic Diagnostic for Face-On B/P Bulges
We present the results of high resolution absorption-line spectroscopy of 3 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_4 of the line-of-sight velocity distribution (LOSVD). In NGC 98, a clear double minimum in h_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_4 minimum in NGC 98 than elsewhere. This more direct method avoids possible artifacts associated with the degeneracy between the measurement of line-of-sight velocity dispersion and h_4.
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Structural properties of disk galaxies: The intrinsic equatorial ellipticity of bulges
The structural parameters of a magnitude-limited sample of 148 unbarred S0-Sb galaxies were derived to study the correlations between bulge and disk parameters as well as the probability distribution function (PDF) of the intrinsic equatorial ellipticity of bulges. A new algorithm (GASP2D) was used to perform the bidimensional bulge-disk decomposition of the J-band galaxy images extracted from the archive of the 2MASS survey. The PDF of intrinsic ellipticities was derived from the distribution of the observed ellipticities of the bulges and misalignments between the the bulges and disks. About 80% of the observed bulges are not oblate but triaxial ellipsoids. Their mean axial ratio in the equatorial plane is =0.85. There is not significant dependence of their PDF on morphology, light concentration or luminosity. This has to be explained by the different scenarios of bulge formation.
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Properties of bars in the local universe
We studied the fraction and properties of bars in a sample of about 3000 galaxies extracted from SDSS-DR5. This represents a volume limited sample with galaxies located between redshift 0.01 -20, and inclination i < 60. Interacting galaxies were excluded from the sample. The fraction of barred galaxies in our sample is 45%. We found that 32% of S0s, 55% of early-type spirals, and 52% of late-type spirals are barred galaxies. The bars in S0s galaxies are weaker than those in later-type galaxies. The bar length and galaxy size are correlated, being larger bars located in larger galaxies. Neither the bar strength nor bar length correlate with the local galaxy density. On the contrary, the bar properties correlate with the properties of their host galaxies. Galaxies with higher central light concentration host less and weaker bars.
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Structural properties of disk galaxies I. The intrinsic ellipticity of bulges
(Abridged) A variety of formation scenarios was proposed to explain the diversity of properties observed in bulges. Studying their intrinsic shape can help in constraining the dominant mechanism at the epochs of their assembly. The structural parameters of a magnitude-limited sample of 148 unbarred S0--Sb galaxies were derived in order to study the correlations between bulges and disks as well as the probability distribution function (PDF) of the intrinsic equatorial ellipticity of bulges. It is presented a new fitting algorithm (GASP2D) to perform the two-dimensional photometric decomposition of galaxy surface-brightness distribution. This was assumed to be the sum of the contribution of a bulge and disk component characterized by elliptical and concentric isophotes with constant (but possibly different) ellipticity and position angles. Bulge and disk parameters of the sample galaxies were derived from the J-band images which were available in the Two Micron All Sky Survey. The PDF of the equatorial ellipticity of the bulges was derived from the distribution of the observed ellipticities of bulges and misalignments between bulges and disks. Strong correlations between the bulge and disk parameters were found. About 80% of bulges in unbarred lenticular and early-to-intermediate spiral galaxies are not oblate but triaxial ellipsoids. Their mean axial ratio in the equatorial plane is = 0.85. There is not significant dependence of their PDF on morphology, light concentration, and luminosity. The interplay between bulge and disk parameters favors scenarios in which bulges assembled from mergers and/or grew over long times through disk secular evolution. But all these mechanisms have to be tested against the derived distribution of bulge intrinsic ellipticities.
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A Study of Catalogued Nearby Galaxy Clusters in the SDSS-DR4: I. Cluster Global Properties
We have selected a sample of 88 nearby (z<0.1) galaxy clusters from the SDSS-DR4 with redshift information for the cluster members. We have derived global properties for each cluster, such as their mean recessional velocity, velocity dispersion, and virial radii. Cluster galaxies have been grouped in two families according to their $u-r$ colours. The total sample consists of 10865 galaxies. As expected, the highest fraction of galaxies (62%) turned to be early-type (red) ones, being located at smaller distances from the cluster centre and showing lower velocity dispersions than late-type (blue) ones. The brightest cluster galaxies are located in the innermost regions and show the smallest velocity dispersions. Early-type galaxies also show constant velocity dispersion profiles inside the virial radius and a mild decline in the outermost regions. In contrast, late-type galaxies show always decreasing velocity dispersions profiles. No correlation has been found between the fraction of blue galaxies and cluster global properties, such as cluster velocity dispersion and galaxy concentration. In contrast, we found correlation between the X-ray luminosity and the fraction of blue galaxies. These results indicate that early- and late-type galaxies may have had different evolution. Thus, blue galaxies are located in more anisotropic and radial orbits than early-type ones. Their star formation seems to be independent of the cluster global properties in low mass clusters, but not for the most massive ones. These observational results suggest that the global environment could be important for driving the evolution of galaxies in the most massive cluster ($σ> 800$ km s$^{-1}$). However, the local environment could play a key role in galaxy evolution for low mass clusters.
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The bar pattern speed of NGC 4431
We present surface photometry and stellar kinematics of NGC 4431, a barred dwarf galaxy in the Virgo cluster undergoing a tidal interaction with one of its neighbors, NGC 4436. We measured its bar pattern speed using the Tremaine-Weinberg method, and derived the ratio of the corotation radius, D_L, to the bar semi-major axis, a_B. We found D_L/a_B=0.6^{+1.2}_{-0.4} at 99% confidence level. Albeit with large uncertainty, the probability that the bar ends close to its corotation radius (i.e., 1.0 \leq D_L/a_B \leq 1.4) is about twice as likely as that the bar is much shorter than corotation radius (i.e., D_L/a_B > 1.4).
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Diffuse Light in Hickson Compact Groups: The Dynamically Young System HCG 44
Compact groups are associations of a few galaxies in which the environment plays an important role in galaxy evolution. The low group velocity dispersion favors tidal interactions and mergers, which may bring stars from galaxies to the diffuse intragroup light. Numerical simulations of galaxy clusters in hierarchical cosmologies show that the amount of the diffuse light increases with the dynamical evolution of the cluster. We search for diffuse light in the galaxy group HCG 44 in order to determine its luminosity and luminosity fraction. Combining with literature data, we aim to constrain the dynamical status of Hickson compact groups. We use Intra Group planetary nebulae (IGPNe) as tracers of diffuse light. These are detected by the so-called on band-off band technique. We found 12 emission line objects in HCG 44, none of them associated with the galaxies of the group. 6/12 emission line objects are consistent with being IGPNe in HCG 44, but are also consistent with being Ly$α$ background galaxies. Thus we derive an upper limit to the diffuse light fraction in HCG 44 of 4.7%. We find a correlation between the fraction of elliptical galaxies and the amount of diffuse light in Hickson compact groups. Those with large fraction of diffuse light are those with large fractions in number and luminosity of E/S0 galaxies. We propose an evolutionary sequence for Hickson compact groups in which the amount of diffuse light increases with the dynamical evolution of the group.
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