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  • 1
    Electronic Resource
    Electronic Resource
    Spectral classification of galaxies
    Amsterdam : Elsevier
    Vistas in Astronomy 38 (1994), S. 287-291 
    Details
    ISSN: 0083-6656
    Keywords: Hubble sequence ; galaxies ; spectral classification
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/0083-6656(94)90039-6
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    Paper (German National Licenses)
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  • 2
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    Strong lensing in the inner halo of galaxy clusters (2016)
    Oxford University Press
    Details
    Publication Date: 2016-06-30
    Description: We present an axially symmetric formula to calculate the probability of finding gravitational arcs in galaxy clusters, being induced by their massive dark matter haloes, as a function of clusters redshifts and virial masses. The formula includes the ellipticity of the clusters dark matter potential by using a pseudo-elliptical approximation. The probabilities are calculated and compared for two dark matter halo profiles, the Navarro, Frenk and White (NFW) and the non-singular-isothermal-sphere (NSIS). We demonstrate the power of our formulation through a Kolmogorov–Smirnov (KS) test on the strong lensing statistics of an X-ray bright sample of low-redshift Abell clusters. This KS test allows us to establish limits on the values of the concentration parameter for the NFW profile ( $c_\Delta$ ) and the core radius for the NSIS profile ( r c ), which are related to the lowest cluster redshift ( z cut ) where strong arcs can be observed. For NFW dark matter profiles, we infer cluster haloes with concentrations that are consistent to those predicted by CDM simulations. As for NSIS dark matter profiles, we find only upper limits for the clusters core radii and thus do not rule out a purely SIS model. For alternative mass profiles, our formulation provides constraints through z cut on the parameters that control the concentration of mass in the inner region of the clusters haloes. We find that z cut is expected to lie in the 0.0–0.2 redshift, highlighting the need to include very low- z clusters in samples to study the clusters mass profiles.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 3
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    An accurate cluster selection function for the J-PAS narrow-band wide-field survey (2016)
    Oxford University Press
    Details
    Publication Date: 2016-01-16
    Description: The impending Javalambre Physics of the accelerating Universe Astrophysical Survey (J-PAS) will be the first wide-field survey of 8500 deg 2 to reach the ‘stage IV’ category. Because of the redshift resolution afforded by 54 narrow-band filters, J-PAS is particularly suitable for cluster detection in the range z 〈1. The photometric redshift dispersion is estimated to be only ~0.003 with few outliers 4 per cent for galaxies brighter than i  ~ 23 AB, because of the sensitivity of narrow band imaging to absorption and emission lines. Here, we evaluate the cluster selection function for J-PAS using N -body+semi-analytical realistic mock catalogues. We optimally detect clusters from this simulation with the Bayesian Cluster Finder, and we assess the completeness and purity of cluster detection against the mock data. The minimum halo mass threshold we find for detections of galaxy clusters and groups with both 〉80 per cent completeness and purity is M h  ~ 5  x  10 13 M up to z  ~ 0.7. We also model the optical observable, $M^{\ast }_{\rm CL}$ –halo mass relation, finding a non-evolution with redshift and main scatter of $\sigma _{M^{\ast }_{\rm CL} | M_{\rm h}}\sim 0.14 \,{\rm dex}$ down to a factor 2 lower in mass than other planned broad-band stage IV surveys, at least. For the M h  ~ 1  x  10 14 M Planck mass limit, J-PAS will arrive up to z  ~ 0.85 with a $\sigma _{M^{\ast }_{\rm CL} | M_{\rm h}}\sim 0.12 \, {\rm dex}$ . Therefore, J-PAS will provide the largest sample of clusters and groups up to z  ~ 0.8 with a mass calibration accuracy comparable to X-ray data.
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    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 4
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    Red sequence of Abell X-ray underluminous clusters (2014)
    Oxford University Press
    Details
    Publication Date: 2014-05-04
    Description: We present an analysis of the colour–magnitude relation for a sample of 56 Abell X-ray underluminous clusters. Our aim is to unveil properties that might elucidate the evolutionary stages of the galaxy populations that compose such systems. To do so, we have compared the parameters of their colour–magnitude relations with the ones found for another sample of 50 normal Abell X-ray emitting clusters, both samples selected in an objective way. The g and r magnitudes from Data Release 7 of the Sloan Digital Sky Survey were used for constructing the colour–magnitude relations. We have found that both samples show the same trend: the red-sequence slopes change with redshift, but the slopes for X-ray underluminous clusters are always flatter than those for normal clusters, with a difference of about 69 per cent along the surveyed redshift range of 0.05 ≤ z  〈 0.20. Also, the intrinsic scatter of the colour–magnitude relation was found to grow with redshift for both samples; however, for the X-ray underluminous clusters, this is systematically larger by about 28 per cent. By applying the Cramér test to the result of this comparison between X-ray normal and underluminous cluster samples, we obtain probabilities of 92 and 99 per cent that the red-sequence slope and intrinsic scatter distributions, respectively, differ, in the sense that X-ray underluminous clusters red sequences show flatter slopes and higher scatters in their relations. No significant differences in the distributions of red-sequence median colours are found between the two cluster samples. This points to X-ray underluminous clusters being younger systems than normal clusters, possibly in the process of accreting groups of galaxies, individual galaxies and gas.
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    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    Photometric Type Ia supernova surveys in narrow-band filters (2014)
    Oxford University Press
    Details
    Publication Date: 2014-09-12
    Description: We study the characteristics of a narrow-band Type Ia supernova (SN) survey through simulations based on the upcoming Javalambre Physics of the accelerating Universe Astrophysical Survey. This unique survey has the capabilities of obtaining distances, redshifts and the SN type from a single experiment thereby circumventing the challenges faced by the resource-intensive spectroscopic follow-up observations. We analyse the flux measurements signal-to-noise ratio and bias, the SN typing performance, the ability to recover light-curve parameters given by the SALT2 model, the photometric redshift precision from Type Ia SN light curves and the effects of systematic errors on the data. We show that such a survey is not only feasible but may yield large Type Ia SN samples (up to 250 SNe at z 〈 0.5 per month of search) with low core-collapse contamination (~1.5 per cent), good precision on the SALT2 parameters (average $\sigma _{m_B}=0.063$ , $\sigma _{x_1}=0.47$ and c = 0.040) and on the distance modulus (average μ = 0.16, assuming an intrinsic scatter int = 0.14), with identified systematic uncertainties sys 0.10 stat . Moreover, the filters are narrow enough to detect most spectral features and obtain excellent photometric redshift precision of z = 0.005, apart from ~2 per cent of outliers. We also present a few strategies for optimizing the survey's outcome. Together with the detailed host galaxy information, narrow-band surveys can be very valuable for the study of SN rates, spectral feature relations, intrinsic colour variations and correlations between SN and host galaxy properties, all of which are important information for SN cosmological applications.
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    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    Retired galaxies: not to be forgotten in the quest of the star formation - AGN connection (2015)
    Oxford University Press
    Details
    Publication Date: 2015-03-20
    Description: We propose a fresh look at the Main Galaxy Sample of the Sloan Digital Sky Survey by packing the galaxies in stellar mass and redshift bins. We show how important it is to consider the emission-line equivalent widths, in addition to the commonly used emission-line ratios, to properly identify retired galaxies (i.e. galaxies that have stopped forming stars and are ionized by their old stellar populations) and not mistake them for galaxies with low-level nuclear activity. We find that the proportion of star-forming galaxies decreases with decreasing redshift in each mass bin, while that of retired galaxies increases. Galaxies with M * 〉 10 11.5 M have formed all their stars at redshift larger than 0.4. The population of AGN hosts is never dominant for galaxy masses larger than 10 10 M . We warn about the effects of stacking galaxy spectra to discuss galaxy properties. We estimate the lifetimes of active galactic nuclei (AGN) relying entirely on demographic arguments – i.e. without any assumption on the AGN radiative properties. We find upper-limit lifetimes of about 1–5 Gyr for detectable AGN in galaxies with masses between 10 10 –10 12 M . The lifetimes of the AGN- dominated phases are a few 10 8  yr. Finally, we compare the star formation histories of star-forming, AGN and retired galaxies as obtained by the spectral synthesis code starlight . Once the AGN is turned on, it inhibits star formation for the next ~0.1 Gyr in galaxies with masses around 10 10 M , ~ 1 Gyr in galaxies with masses around 10 11 M .
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    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    Galaxy triplets in Sloan Digital Sky Survey Data Release 7 - II. A connection with compact groups? (2013)
    Oxford University Press
    Details
    Publication Date: 2013-07-26
    Description: We analyse a sample of 71 triplets of luminous galaxies derived from the work of O’Mill et al. We compare the properties of triplets and their members with those of control samples of compact groups, the 10 brightest members of rich clusters and galaxies in pairs. The triplets are restricted to have members with spectroscopic redshifts in the range 0.01 ≤ z  ≤ 0.14 and absolute r -band luminosities brighter than M r  = –20.5. For these member galaxies, we analyse the stellar mass content, the star formation rates, the D n (4000) parameter and ( M g  – M r ) colour index. Since galaxies in triplets may finally merge in a single system, we analyse different global properties of these systems. We calculate the probability that the properties of galaxies in triplets are strongly correlated. We also study total star formation activity and global colours, and define the triplet compactness as a measure of the percentage of the system total area that is filled by the light of member galaxies. We concentrate in the comparison of our results with those of compact groups to assess how the triplets are a natural extension of these compact systems. Our analysis suggests that triplet galaxy members behave similarly to compact group members and galaxies in rich clusters. We also find that systems comprising three blue, star-forming, young stellar population galaxies (blue triplets) are most probably real systems and not a chance configuration of interloping galaxies. The same holds for triplets composed of three red, non-star-forming galaxies, showing the correlation of galaxy properties in these systems. From the analysis of the triplet as a whole, we conclude that, at a given total stellar mass content, triplets show a total star formation activity and global colours similar to compact groups. However, blue triplets show a high total star formation activity with a lower stellar mass content. From an analysis of the compactness parameter of the systems we find that light is even more concentrated in triplets than in compact groups. We propose that triplets composed of three luminous galaxies, should not be considered as an analogous of galaxy pairs with a third extra member, but rather they are a natural extension of compact groups.
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    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    Dissecting galaxy triplets in the Sloan Digital Sky Survey Data Release 10 - I. Stellar populations and emission line analysis (2016)
    Oxford University Press
    Details
    Publication Date: 2016-05-05
    Description: We identify isolated galaxy triplets in a volume-limited sample from the Sloan Digital Sky Survey Data Release 10. Our final sample has 80 galaxy systems in the redshift range 0.04 ≤ z ≤ 0.1, brighter than M r = –20.5 + 5 log h 70 . Spectral synthesis results and WHAN and BPT diagnostic diagrams were employed to classify the galaxies in these systems as star-forming, active nuclei, or passive/retired. Our results suggest that the brightest galaxies drive the triplet evolution, as evidenced by the strong correlations between properties as mass assembly and mean stellar population age with triplet properties. Galaxies with intermediate luminosity or the faintest one within the triplet seem to play a secondary role. Moreover, the relation between age and stellar mass of galaxies is similar for these galaxies but different for the brightest galaxy in the system. Most of the triplet galaxies are passive or retired, according to the WHAN classification. Low-mass triplets present different fractions of WHAN classes when compared to higher mass triplets. A census of WHAN class combinations shows the dominance of star-forming galaxies in low-mass triplets while retired and passive galaxies prevail in high-mass systems. We argue that these results suggest that the local environment, through galaxy interactions driven by the brightest galaxy, is playing a major role in triplet evolution.
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    Topics: Physics
    Published by Oxford University Press
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  • 9
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    Testing phenomenological and theoretical models of dark matter density profiles with galaxy clusters (2013)
    Oxford University Press
    Details
    Publication Date: 2013-11-17
    Description: We use the stacked gravitational lensing mass profile of four high-mass ( M 10 15 M ) galaxy clusters around z 0.3 from Umetsu et al. to fit density profiles of phenomenological [Navarro–Frenk–White (NFW), Einasto, Sérsic, Stadel, Baltz–Marshall–Oguri (BMO) and Hernquist] and theoretical (non-singular Isothermal Sphere, DARKexp and Kang & He) models of the dark matter distribution. We account for large-scale structure effects, including a two-halo term in the analysis. We find that the BMO model provides the best fit to the data as measured by the reduced 2 . It is followed by the Stadel profile, the generalized NFW profile with a free inner slope and by the Einasto profile. The NFW model provides the best fit if we neglect the two-halo term, in agreement with results from Umetsu et al. Among the theoretical profiles, the DARKexp model with a single form parameter has the best performance, very close to that of the BMO profile. This may indicate a connection between this theoretical model and the phenomenology of dark matter haloes, shedding light on the dynamical basis of empirical profiles which emerge from numerical simulations.
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    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 10
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    The nature of extremely red galaxies in the local universe (2013)
    Oxford University Press
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    Publication Date: 2013-08-22
    Description: We investigate the nature of extremely red galaxies (ERGs), objects whose colours are redder than those found in the red sequence present in colour–magnitude diagrams of galaxies. We selected from the Sloan Digital Sky Survey Data Release 7 a volume-limited sample of such galaxies in the redshift interval 0.010 〈 z  〈 0.030, brighter than M r  = –17.8 (magnitudes dereddened, corrected for the Milky Way extinction) and with ( g – r ) colours larger than those of galaxies in the red sequence. This sample contains 416 ERGs, which were classified visually. Our classification was cross-checked with other classifications available in the literature. We found from our visual classification that the majority of objects in our sample are edge-on spirals (73 per cent). Other spirals correspond to 13 per cent, whereas elliptical galaxies comprise only 11 per cent of the objects. After comparing the morphological mix and the distributions of Hα/Hβ and axial ratios of ERGs and objects in the red sequence, we suggest that dust, more than stellar population effects, is the driver of the red colours found in these extremely red galaxies.
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    Topics: Physics
    Published by Oxford University Press
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