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1.
High-resolution CO maps are an essential tool to search for observational evidence of AGN fueling in galaxy nuclei. While their capabilities will be surpassed by ALMA, current mm-interferometers can already provide relevant information on scales which are critical for the process of angular momentum transfer in fueling the AGN. In this context we present the latest results issued from the NUclei of GAlaxies (NUGA) project, a high-resolution (0.5′′–1′′) CO survey of low luminosity AGNs conducted with the IRAM Plateau de Bure interferometer (PdBI). The use of more specific molecular tracers of dense gas can probe the feedback influence of activity on the chemistry and energy balance in the interstellar medium of nearby galaxies, a prerequisite to understanding how feedback operate at higher redshift galaxies. We discuss the results obtained in an ongoing study devoted to probe the feedback of activity from nearby Seyferts to high-redshift QSO.  相似文献   

2.
According to the new preheating mechanism of galaxy formation suggested by Mo et al., we construct a simple model of formation of disk galaxies within the current paradigm of galaxy formation. It incorporates preheating, gas cooling, bulge formation and star for-mation. The predicted stellar and HI mass functions of galaxies are discussed and compared with the observations. It is found that our model can roughly match both the observed galaxy luminosity function and the observed HI-mass function.  相似文献   

3.
Co-evolution of Galaxies and AGNs in Hierarchical Galaxy Formation Models   总被引：1，自引：0，他引：1  
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4.
Research on two-dimensional (2-D) properties of galaxies is a significant component of the study of galaxy formation and evolution. Through the spatial distribution of physical properties (derived from integrated luminosity and spectroscopy) of galaxies, we are allowed to realize the inner environment and evolution history of each individual galaxy and finally answer how galaxies were assembled. In this paper, with reviewing previous work, we present a proposal for study on 2-D properties of nearby galaxies. In our prospective work, we will make use of multi-wavelength data covering a range from ultraviolet to far-infrared to determine the distributions of properties such as age, metallicity and dust-reddening in nearby galaxies, and try to remove the degeneracy among them. Combining with surface photometry and spectroscopy, we will also analyze the distribution of HII regions and star formation properties in galaxies. In our future plan, the World Space Observatory for Ultraviolet (WSO/UV) will be applied to our research and allow detail diagnosis of nearby galaxies at ultraviolet band.  相似文献   

5.
Luminous and Ultraluminous infrared galaxies (ULIRGs) contain the most intense regions of star formation in the local universe. Because molecular gas is the fuel for current and future star formation, the physical properties and distribution of the warm, dense molecular gas are key components for understanding the processes and timescales controlling star formation in these merger and merger remnant galaxies. We present new results from a legacy project on the Submillimeter Array which is producing high resolution images of a representative sample of galaxies with log L FIR >11.4 and D<200 Mpc.  相似文献   

6.
Understanding the formation and evolution of massive galaxies provides important keys to constrain the baryon assembly processes in the ΛCDM hierarchical scenario. We review the main results obtained so far with the K20 and other recent near-IR surveys on the redshift distribution, the evolution of the luminosity function and luminosity density, the nature of old and dusty EROs, the evolution of the galaxy stellar mass function and the nature of luminous starbursts at z∼2 which may be the progenitors of the present-day massive spheroidal galaxies.  相似文献   

7.
A composite sample of NIR-selected galaxies having extended multicolor coverage has been used to probe the cosmological evolution of the blue luminosity function and of the stellar mass function. The bright fraction of the sample has spectroscopic redshifts, and the remaining fraction well-calibrated photometric redshifts. The resulting blue luminosity function shows an increasing brightening with redshift respect to the local luminosity function. Hierarchical CDM models predictions are in agreement only at low and intermediate redshifts but fail to reproduce the observed brightening at high redshifts (z ∼ 2–3). This brightening marks the epoch where starburst activity triggered by galaxy interactions could be an important physical mechanism for the galaxy evolution. At the same time the NIR galaxy sample has been used to trace the evolution of the cosmological stellar mass density up to ∼3. A clear decrease of the average mass density is apparent with a fraction ∼15% of the local value at z ∼ 3. UV bright star-forming galaxies are substancial contributors to the evolution of the stellar mass density. Although these results are globally consistent with Λ–CDM scenarios, they tend to underestimate the mass density produced by more massive galaxies present at z > 2.  相似文献   

8.
We report on observations, with sub-parsec resolution, of neutral hydrogen seen in absorption in the λ=21 cm line against the nucleus of the active spiral galaxy NGC 5793. The absorption line consists of three components separated in both location as well as velocity. We derive HI column densities of 2×1022 cm−2 assuming a gas spin temperature of 100 K. For the first time we are able to reliably estimate the HI cloud sizes (≈15 pc) and atomic gas densities (≈200 cm−3). Our results suggest that the HI gas is not associated with the <10 pc region which presumably contains the H2O masers, but it is more distant from the nucleus, and is probably associated with the r1 kpc gas seen in CO.  相似文献   

9.
Observations are presented of the isolated dwarf irregular galaxy And IV made with the Hubble Space Telescope Advanced Camera for Surveys and the Giant Metrewave Radio Telescope in the 21 cm HI line. We determine the galaxy distance of 7.17 ± 0.31 Mpc using the Tip of Red Giant Branch method. The galaxy has a total blue absolute magnitude of –12.81 mag, linear Holmberg diameter of 1.88 kpc, and an HI ‐disk extending to 8.4 times the optical Holmberg radius. The HI massto‐blue luminosity ratio for And IV amounts 12.9 M⊙/L⊙. From the GMRT data we derive the rotation curve for the HI and fit it with different mass models. We find that the data are significantly better fit with an iso‐thermal dark matter halo, than by an NFW halo. We also find that MOND rotation curve provides a very poor fit to the data. The fact that the isothermal dark matter halo provides the best fit to the data supports models in which star formation feedback results in the formation of a dark matter core in dwarf galaxies. The total mass‐to‐blue luminosity ratio of 162 M⊙/L⊙ makes And IV among the darkest dIrr galaxies known. However, its baryonic‐to‐dark mass ratio (Mgas + M *)/MT = 0.11 is close to the average cosmic baryon fraction of 0.15. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

10.
Using the recently completed Giant Meterwave Radio Telescope, we have detected the HI 21 cm-line absorption from the peculiar galaxy C153 in the galaxy cluster Abell 2125. The HI absorption is at a redshift of 0.2533, with a peak optical depth of 0.36. The full width at half minimum of the absorption line is 100 km s−1. The estimated column density of atomic Hydrogen is 0.7×1022(T s /100) cm−2. The HI absorption is redshifted by ∼400km s−1 compared to the [OIII] emission line from this system. We attribute this to an infalling cold gas or to an out-flowing ionised gas, or to a combination of both as a consequence of tidal interactions of C153 with either a cluster galaxy or the cluster potential.  相似文献   

11.
Molecular line emission is a useful tool for probing the highly obscured inner kpc of starburst galaxies and buried AGNs. Molecular line ratios serve as diagnostic tools of the physical conditions of the gas—but also of its chemical properties. Both provide important clues to the type and evolutionary stage of the nuclear activity. While CO emission remains the main tracer for molecular distribution and dynamics, molecules such as HCN, HNC, HCO+, CN and HC3N are useful for probing the properties of the denser (n≳104 cm−3), star-forming gas. Here I discuss current views on how line emission from these species can be interpreted in luminous galaxies. HNC, HCO+ and CN are all species that can be associated both with photon dominated regions (PDRs) in starbursts—as well as X-ray dominated regions (XDRs) associated with AGN activity. HC3N line emission may identify galaxies where the starburst is in the early stage of its evolution.  相似文献   

12.
We explore the evolution of the early-type galaxy population in the rich cluster Abell 2390 at z=0.23. For this purpose, we have obtained spectroscopic data of 51 elliptical and lenticular galaxies with MOSCA at the 3.5 m telescope on Calar Alto Observatory. As our investigation spans both a broad range in luminosity (–22.3≤MB≤–:19.3)and a wide field of view (10′×10′), the environmental dependence of different formation scenarios can be analysed in detail as a function of radius from the cluster center. In this paper, we present first results on the Faber-Jackson relation and, for a subsample of 14 galaxies with morphological and structural parameters from HST, we also investigate the evolution of the Kormendy relation and the Fundamental Plane. We find a mild luminosity evolution of the early-type galaxies in Abell 2390: our objects are on average brighter by m B∼0.4 mag. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

13.
The Eridanus galaxies follow the well-known radio—FIR correlation. The majority (70%) of these galaxies have their star formation rates below that of the Milky Way. The galaxies that have a significant excess of radio emission are identified as low luminosity AGNs based on their radio morphologies obtained from the GMRT observations. There are no powerful AGNs (L 20cm > 1023 W Hz−1) in the group. The two most far-infrared and radio luminous galaxies in the group have optical and HI morphologies suggestive of recent tidal interactions. The Eridanus group also has two far-infrared luminous but radio-deficient galaxies. It is believed that these galaxies are observed within a few Myr of the onset of an intense star formation episode after being quiescent for at least a 100 Myr. The upper end of the radio luminosity distribution of the Eridanus galaxies (L 20cm ∼ 1022 W Hz−1) is consistent with that of the field galaxies, other groups, and late-type galaxies in nearby clusters.  相似文献   

14.
The sample of nearby LIRGs and ULIRGs for which dense molecular gas tracers have been measured is building up, allowing for the study of the physical and chemical properties of the gas in the variety of objects in which the most intense star formation and/or AGN activity in the local universe is taking place. This characterisation is essential to understand the processes involved, discard others and help to interpret the powerful starbursts and AGNs at high redshift that are currently being discovered and that will routinely be mapped by ALMA. We have studied the properties of the dense molecular gas in a sample of 17 nearby LIRGs and ULIRGs through millimeter observations of several molecules (HCO+, HCN, CN, HNC and CS) that trace different physical and chemical conditions of the dense gas in these extreme objects. In this paper we present the results of our HCO+ and HCN observations. We conclude that the very large range of measured line luminosity ratios for these two molecules severely questions the use of a unique molecular tracer to derive the dense gas mass in these galaxies.  相似文献   

15.
We present the first attempt at measuring the production rate of tidal dwarf galaxies (TDGs) and estimating their contribution to the overall dwarf population. Using HST/ACS deep imaging data from GOODS and GEMS surveys in conjunction with photometric redshifts from COMBO-17 survey, we performed a morphological analysis for a sample of merging/interacting galaxies in the Extended Chandra Deep Field South and identified tidal dwarf candidates in the rest-frame optical bands. We estimated a production rate about 1.4×10−5 per Gyr per comoving volume for long-lived TDGs with stellar mass 3×108−9 M⊙ at 0.5<z<1.1. Together with galaxy merger rates and TDG survival rate from the literature, our results suggest that only a marginal fraction (less than 10%) of dwarf galaxies in the local universe could be tidally-originated. TDGs in our sample are on average bluer than their host galaxies in the optical. Stellar population modelling of optical to near-infrared spectral energy distributions (SEDs) for two TDGs favors a burst component with age 400/200 Myr and stellar mass 40%/26% of the total, indicating that a young stellar population newly formed in TDGs. This is consistent with the episodic star formation histories found for nearby TDGs.  相似文献   

16.
We discuss observations of the first galaxies, within cosmic reionization, at centimeter and millimeter wavelengths. We present a summary of current observations of the host galaxies of the most distant QSOs (z∼6). These observations reveal the gas, dust, and star formation in the host galaxies on kpc-scales. These data imply an enriched ISM in the QSO host galaxies within 1 Gyr of the big bang, and are consistent with models of coeval supermassive black hole and spheroidal galaxy formation in major mergers at high redshift. Current instruments are limited to studying truly pathologic objects at these redshifts, meaning hyper-luminous infrared galaxies (L FIR ∼1013 L ⊙). ALMA will provide the one to two orders of magnitude improvement in millimeter astronomy required to study normal star forming galaxies (i.e. Ly-α emitters) at z∼6. ALMA will reveal, at sub-kpc spatial resolution, the thermal gas and dust—the fundamental fuel for star formation—in galaxies into cosmic reionization.  相似文献   

17.
The atomic and molecular hydrogen gas properties of a complete sample of Markarian galaxies with flux density at 60 µm higher than 1.95 Jy are presented. We present the improved far-infrared luminosity function of Markarian galaxies; and its comparison with other samples. We find that 40% of the bright IRAS galaxies of far-infrared luminosity higher than 1010.5 L are Markarian galaxies. There is an absence of correlation between HI content of Markarian galaxies and current star formation activity, implying that star formation in these systems has complex structure and it is not a simple function of the HI content. On the contrary, the H2 content of Markarian galaxies is well correlated with star formation activity. It is argued that tight correlation between HI and H2 contents is a consequence of transformation of atomic hydrogen into molecular.Published in Astrofizika, Vol. 38, No. 4, pp. 636–644, October–December, 1995.  相似文献   

18.
We summarize our modelling of galaxy photometric evolution (the GRASIL code). By including the effects of dust grains and PAH molecules in a two-phase clumpy medium, where clumps are associated with star-forming regions, we reproduce the observed UV to radio SEDs of galaxies with star formation rates from zero to several hundred M ⊙ yr-1.GRASIL is a powerful tool for investigating star formation, the initial mass function and the supernova rate in nearby starbursts and normal galaxies, as well as for predicting the evolution of luminosity functions of different types of galaxies at wavelengths covering six decades. It may be interfaced with any device to provide the star formation and metallicity histories of a galaxy. As an application, we have investigated the properties of early-type galaxies in the HDF, tracking the contribution of this population to the cosmic star formation history, which has a broad peak between z = 1.5 and 4.To explain the absence of objects at z ≳ 1.3, we suggest a sequence of dust-enshrouded merger-driven starbursts in the first few Gyr of galaxy lifetimes. We are at present working on a complementary sample of late-type objects selected in a similar way. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

19.
We present the first observations of molecular line emission in NGC 3718 with the IRAM 30m and the Plateau de Bure Interferometer. This galaxy is an excellent example for a strongly warped gas disk harboring an active galactic nucleus (AGN). An impressive dust lane is crossing the nucleus and a warp is developing into a polar ring. The molecular gas content is found to be typical of an elliptical galaxy with a relatively low molecular gas mass content (∼ 4 × 108 M ⊙). The molecular gas distribution is found to warp from the inner disk together with the HI distribution. The CO data were also used to improve the kinematic modeling in the inner part of the galaxy, based on the so-called tilted ring-model. The nature of NGC 3718 is compared with its northern sky `twin' Centaurus A and the possible recent swallowing of a small-size gas-rich spiral is discussed. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

20.
Using an apparent-magnitude limited Main galaxy sample of the Sloan Digital Sky Survey Data Release 7(SDSS DR7), we investigate the correlation between morphologies and luminosity for the Main galaxy sample. Our Main galaxy sample is divided into two classes: Main galaxies only with TARGET_GALAXY flag (bestPrimtarget = 64), and ones also with other flags. It is found that for the second class Main galaxies, the early-type proportion monotonously increases with increasing luminosity nearly in the whole luminosity region. But for the first class Main galaxies, the early-type proportion increases with increasing luminosity only within a certain luminosity region (−22.2 < M r  < −19.8). In the high luminosity region (M r  < −22.2), the early-type proportion of the first class Main galaxies even decreases dramatically with increasing luminosity. We also analyze the correlation between morphologies and luminosity of galaxies around the peak of the redshift distribution ( 0.07 ≤ z ≤ 0.08 ). In such a narrow redshift region, we still observe strong correlation between morphologies and luminosity, which shows that this correlation is fundamental.  相似文献   

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