191 research outputs found
Micromammals from the late early Miocene of capak (western Anatolia) herald a time of change
No full textThe new fossil micromammal assemblage of capak represents a mixture of both Anatolian and European faunal elements. The locality is very important for understanding faunal evolution in the less well-known time interval at the end of the early Miocene of western Anatolia. In capak, nine species of rodents and one species of ochotonid were encountered: the hamsters Democricetodon gracilis, Megacricetodon primitivus, Eumyarion aff. E. montanus, Cricetodon cf. C. aliveriensis, Cricetodon sp., and Karydomys cf. K. strati, the mole-rat Debruijnia sp., the squirrel Aliveria luteyni, the dormouse Myomimus tanjuae n. sp., and the pika Albertona balkanica. The assemblage is referable to Anatolian local zone E or MN unit 4. The relative abundance of the various genera is markedly different from that of the older early Miocene assemblages, suggesting that the environment in Anatolia became drier and had a more open landscape. UUID: http://zoobank.org/75f3276c-dcd8-4090-b2f6-d8fc8d3c3f7cNational Geographic grant Palaeogeography of Mammals Following the Collision of the African and Eurasian Plates [GEFNE 140-15]; Ege University [TTM/001/2016, TTM/002/2016, UK/123/2019, UK/145/2020]; Scientific Grant Agency of the Ministry of Education, Science, Research and Sport of the Slovak Republic [VEGA 1/0164/19, 1/0533/21]; Slovak Research and Development Agency [APVV-15-0575, APVV-16-0121]; FEDER/Ministerio de Ciencia e Innovacion-Agencia Estatal de Investigacion [PGC2018-094122-B-I00]This work was funded by National Geographic grant Palaeogeography of Mammals Following the Collision of the African and Eurasian Plates (GEFNE 140-15). This study was supported by Ege University (TTM/001/2016) and (TTM/002/2016) to SM and MB. This study was also supported by grants UK/123/2019, UK/145/2020; Scientific Grant Agency of the Ministry of Education, Science, Research and Sport of the Slovak Republic VEGA 1/0164/19, 1/0533/21, and by the Slovak Research and Development Agency under contract Nos. APVV-15-0575 and APVV-16-0121. This work was partially supported by project PGC2018-094122-B-I00 funded by FEDER/Ministerio de Ciencia e Innovacion-Agencia Estatal de Investigacion
An ALMA survey of submillimeter galaxies in the COSMOS field: Multiwavelength counterparts and redshift distribution
No full textWe carried out targeted ALMA observations of 129 fields in the COSMOS region at 1.25 mm, detecting 152 galaxies at S/N ≥ 5with an average continuum RMS of 150 μJy. These fields represent a S/N-limited sample of AzTEC/ASTE sources with 1.1 mm S/N≥ 4 over an area of 0.72 square degrees. Given ALMA’s fine resolution and the exceptional spectroscopic and multiwavelength photometric data available in COSMOS, this survey allows us unprecedented power in identifying submillimeter galaxy counterparts and determining their redshifts through spectroscopic or photometric means. In addition to 30 sources with prior spectroscopic redshifts, we identified redshifts for 113 galaxies through photometric methods and an additional nine sources with lower limits, which allowed a statistically robust determination of the redshift distribution. We have resolved 33 AzTEC sources into multi-component systems and our redshifts suggest that nine are likely to be physically associated. Our overall redshift distribution peaks at z ~ 2.0 with a high-redshift tail skewing the median redshift to z = 2.48 ± 0.05. We find that brighter millimeter sources are preferentially found at higher redshifts. Our faintestsources, with S_(1.25 mm) 1.8 mJy, have a median redshift of z = 3.08 ± 0.17. After accounting for spectral energy distribution shape and selection effects, these results are consistent with several previous submillimeter galaxy surveys, and moreover, support the conclusion that the submillimeter galaxy redshift distribution is sensitive to survey depth
Reconciling mass functions with the star-forming main sequence via mergers
No full textWe combine star formation along the ‘main sequence’, quiescence and clustering and merging to produce an empirical model for the evolution of individual galaxies. Main-sequence star formation alone would significantly steepen the stellar mass function towards low redshift, in sharp conflict with observation. However, a combination of star formation and merging produces a consistent result for correct choice of the merger rate function. As a result, we are motivated to propose a model in which hierarchical merging is disconnected from environmentally independent star formation. This model can be tested via correlation functions and would produce new constraints on clustering and merging
High-Redshift Protoclusters Traced by Submillimeter Galaxies: Tracing Star Formation Activity out to z > 4
No full textClustering analysis indicate that at z ~ 2 submm-selected galaxies (SMGs) reside in very massive halos (M_(DM) > 5 × 10^(13)), suggesting that SMGs trace high-density environments that evolve into rich galaxy clusters. Conversely, recent work suggests that SMGs are tracers of a broader range of environments, including structures with more modest masses caught in highly active periods; since galaxies in these structures are likely caught during episodes of peak starbursts, SMGs may be tracers of a wider range of environments beyond the progenitors of todays very rich clusters, opening a window for a more complete exploration of the details underpinning the process of galaxy evolution in concert with the assembly of the large scale structure (LSS). We have undertaken a large observing program comprising deep narrow-band Ly-alpha imaging and multi-object spectroscopy using Palomar/Keck/Magellan/Gemini telescopes to probe for galaxy overdensities in SMG environments at z ~ 1 − 5. With ~200 spectroscopically-confirmed Ly-alpha emitters, we are in a position to gauge the level of galaxy overdensity in these regions
A Tight Relation between N/O Ratio and Galaxy Stellar Mass Can Explain the Evolution of Strong Emission Line Ratios with Redshift
No full textThe offset of high-redshift star-forming galaxies in the [O III]/Hβ versus [N II]/Hα (O3N2) diagram in comparison with the local star-forming galaxy sequence is now well established. The physical origin of the shift is the subject of some debate and has important implications for metallicity measurements based on strong lines at all redshifts. To investigate the origin of the O3N2 offset, we use a sample of ~100,000 star-forming galaxies from the Sloan Digital Sky Survey DR12 to understand how measurable galaxy physical properties (Σ_(SFR), ionization parameter, nitrogen-to-oxygen (N/O) ratio, and stellar mass) drive galaxy position in two key diagnostic diagrams: O3N2 and [O III]/Hβ versus [S II]/Hα (O3S2). At fixed [O III]/Hβ, galaxies close to the high-redshift locus in O3N2 have higher Σ_(SFR), stellar mass, and N/O ratio. We conclude that higher N/O ratios at fixed [O III]/Hβ are the proximate cause of the O3N2 shift. We also find a tight correspondence in the distributions of stellar mass and N/O in the diagnostic diagrams. This relation, spanning a range of galaxy evolutionary states, suggests that the N/O–M* relation is more fundamental than the relation between N/O and O/H. We argue that a more fundamental N/O–M* relation is well-motivated physically. Because the mass–metallicity relation evolves more rapidly with redshift than N/O–M*, the N/O ratios of high-redshift galaxies are elevated in comparison with local galaxies with the same gas-phase O/H. The O3N2 shift and elevated N/O ratios observed in high-redshift galaxies, therefore, come about as a natural consequence of the N/O–M* relation combined with the evolution of the mass–metallicity relation
Chandra centres for COSMOS X-ray galaxy groups: differences in stellar properties between central dominant and offset brightest group galaxies
No full textWe present the results of a search for galaxy clusters and groups in the ∼2 deg^2 of the COSMOS field using all available X-ray observations from the XMM–Newton and Chandra observatories. We reach an X-ray flux limit of 3×10^(−16) erg cm^(−2)s^(−1) in the 0.5–2 keV range, and identify 247 X-ray groups with M_(200c) = 8×10^(12) -3×10^(14)M⊙ at a redshift range of 0.08 ≤ z < 1.53, using the multiband photometric redshift and the master spectroscopic redshift catalogues of the COSMOS. The X-ray centres of groups are determined using high-resolution Chandra imaging. We investigate the relations between the offset of the brightest group galaxies (BGGs) from halo X-ray centre and group properties and compare with predictions from semi-analytic models and hydrodynamical simulations. We find that BGG offset decreases with both increasing halo mass and decreasing redshift with no strong dependence on the X-ray flux and SNR. We show that the BGG offset decreases as a function of increasing magnitude gap with no considerable redshift-dependent trend. The stellar mass of BGGs in observations extends over a wider dynamic range compared to model predictions. At z < 0.5, the central dominant BGGs become more massive than those with large offsets by up to 0.3 dex, in agreement with model prediction. The observed and predicted log-normal scatter in the stellar mass of both low- and large-offset BGGs at fixed halo mass is ∼0.3 dex
Magellan spectroscopy of AGN candidates in the COSMOS field
No full textWe present spectroscopic redshifts for the first 466 X-ray- and radio-selected AGN targets in the 2 deg2 COSMOS field. Spectra were obtained with the IMACS instrument on the Magellan (Baade) telescope, using the nod-and-shuffle technique. We identify a variety of type 1 and type 2 AGNs, as well as red galaxies with no emission lines. Our redshift yield is 72% down to iAB=24, although the yield is >90% for iAB<22. We expect the completeness to increase as the survey continues. When our survey is complete and additional redshifts from the zCOSMOS project are included, we anticipate ~1100 AGNs with redshifts over the entire COSMOS field. Our redshift survey is consistent with an obscured AGN population that peaks at z~0.7, although further work is necessary to disentangle the selection effects. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555 and based on data collected at the Magellan Telescope, which is operated by the Carnegie Observatories
The VIMOS Ultra Deep Survey: 10 000 Galaxies to Study the Early Phases of Galaxy Assembly at 2 < z < 6+
No full textThe VIMOS Ultra Deep Survey (VUDS)
aims to study the early phases of
galaxy
assembly from a large, well-defined
sample of ~ 10 000 galaxies
with spectra obtained from very deep
VIMOS observations. This sample is
by far the largest to date, with spectroscopic
redshifts covering a redshift
range 2 < z < ~ 6 and it enables a range
of fundamental studies to better understand
the first major steps in galaxy
evolution. The first results from the
VUDS survey are summarised, including
the discovery of a galaxy protocluster
at z = 3.3
An Alternate Approach to Measure Specific Star Formation Rates at
No full textApJ acceptedInternational audienceWe trace the specific star formation rate (sSFR) of massive star-forming galaxies () from to 7. Our method is substantially different from previous analyses, as it does not rely on direct estimates of star formation rate, but on the differential evolution of the galaxy stellar mass function (SMF). We show the reliability of this approach by means of semi-analytical and hydrodynamical cosmological simulations. We then apply it to real data, using the SMFs derived in the COSMOS and CANDELS fields. We find that the sSFR is proportional to at , in agreement with other observations but in tension with the steeper evolution predicted by simulations from to 2. We investigate the impact of several sources of observational bias, which however cannot account for this discrepancy. Although the SMF of high-redshift galaxies is still affected by significant errors, we show that future large-area surveys will substantially reduce them, making our method an effective tool to probe the massive end of the main sequence of star-forming galaxies
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