arXiv subjects

Hong Wu

Publications and source records attributed to Hong Wu.

At least 163 records · Page 9Linked to original sources

arXiv2011

Star Formation Properties in Barred Galaxies (SFB). II. NGC 2903 and NGC 7080

Stellar bars are important for the secular evolution of disk galaxies because they can drive gas into the galactic central regions. To investigate the star formation properties in barred galaxies, we presented a multi-wavelength study of two barred galaxies NGC 2903 and NGC 7080. We performed the three-component bulge-disk-bar decomposition using the 3.6 μm images, and identified the bulges in the two galaxies as pseudobulges. Based on the narrowband Hα images, the star formation clumps were identified and analyzed. the clumps in the bulge regions have the highest star formation rate surface densities in both galaxies, while the star formation activities in the bar of NGC 2903 are more intense than those in the bar of NGC 7080. Finally, we compared with the scenario of bar-driven secular evolution in previous studies, and discussed the possible evolutionary stages of the two galaxies.

astro-ph.CO↗

arXiv2011

Spectroscopic Study of Globular Clusters in the Halo of M31 with Xinglong 2.16m Telescope

We present the spectroscopic observations for 11 confirmed globular clusters of M31 with the OMR spectrograph on 2.16m telescope at Xinglong site of National Astronomical Observatories, Chinese Academy of Sciences. Nine of our sample clusters are located in the halo of M31 and the most remote one is out to a projected radius of 78.75 kpc from the galactic center. For all our sample clusters, we measured the Lick absorption-line indices and the radial velocities. It is noted that most GCs of our sample are distinct from the HI rotation curve of M31 galaxy, especially for B514, MCGC5, H12 and B517, suggesting that most of our sample clusters do not have kinematic association with the star forming young disk of the galaxy. We fitted the absorption line indices with the updated stellar population model Thomas et al. (2010) with two different tracks of Cassisi and Padova, separately, by applying the $χ^2-$minimization method. The fitting results show that all our sample clusters are older than 10 Gyr, and metal-poor ($-0.91 \le $ [Fe/H] $\le -2.38$ dex). After merging the spectroscopic metallicity of our work with the previously published ones, we extended the cluster sample out to a projected radius of 117 kpc from the galaxy's center. We found the metallicity gradient for all the confirmed clusters exists with a slope of $-0.028\pm0.001$ dex kpc$^{-1}$. However, the slope turns to be $-0.018\pm0.001$ dex kpc$^{-1}$ for all the halo clusters, which is much shallower. If we only consider the outer halo clusters with $r_{\rm p}>25$ kpc, the slope becomes $-0.010\pm0.002$ dex kpc$^{-1}$ and if one cluster G001 is excluded from the outer halo sample, the slope is $-0.004\pm0.002$ dex kpc$^{-1}$. Thus we conclude that metallicity gradient for M31 outer halo clusters is not significant, which agrees well with the previous findings.

astro-ph.CO↗

arXiv2011

Star Formation Properties in Barred Galaxies(SFB). I. Ultraviolet-to-Infrared Imaging and Spectroscopic Studies of NGC 7479

Large-scale bars and minor mergers are important drivers for the secular evolution of galaxies. Based on ground-based optical images and spectra as well as ultraviolet data from the Galaxy Evolution Explorer and infrared data from the Spitzer Space Telescope, we present a multi-wavelength study of star formation properties in the barred galaxy NGC 7479, which also has obvious features of a minor merger. Using various tracers of star formation, we find that under the effects of both a stellar bar and a minor merger, star formation activity mainly takes place along the galactic bar and arms, while the star formation rate changes from the bar to the disk. With the help of spectral synthesis, we find that strong star formation took place in the bar region about 100 Myr ago, and the stellar bar might have been $\sim$10 Gyr old. By comparing our results with the secular evolutionary scenario from Jogee et al., we suggest that NGC 7479 is possibly in a transitional stage of secular evolution at present, and it may eventually become an earlier type galaxy or a luminous infrared galaxy. We also note that the probable minor merger event happened recently in NGC 7479, and we find two candidates for minor merger remnants.

astro-ph.CO↗

arXiv2010

Eight new quasars discovered by LAMOST in one extragalactic field

We report the discovery of eight new quasars in one extragalactic field (five degree centered at RA=$08^h58^m08.2^s$, Dec=$01^o32'29.7''$) with the LAMOST commissioning observations on December 18, 2009. These quasars, with $i$ magnitudes from 16.44 to 19.34 and redshifts from 0.898 to 2.773, were not identified in the SDSS spectroscopic survey, though six of them with redshifts less than 2.5 were selected as quasar targets in SDSS. Except one source without near-IR $Y$-band data, seven of these eight new quasars meet a newly proposed quasar selection criterion involving both near-IR and optical colors. Two of them were found in the 'redshift desert' for quasars ($z$ from 2.2 to 3), indicating that the new criterion is efficient for recovering the missing quasars with similar optical colors as stars. Although LAMOST met some problems during the commissioning observations, we were still able to identify other 38 known SDSS quasars in this field, with $i$ magnitudes from 16.24 to 19.10 and redshifts from 0.297 to 4.512. Our identifications imply that a substantial fraction of quasars may be missing in the previous quasar surveys. The implication of our results to the future LAMOST quasar survey is discussed.

astro-ph.CO↗

arXiv2010

A very bright i=16.44 quasar in the `redshift desert' discovered by LAMOST

The redshift range from 2.2 to 3, is known as the 'redshift desert' of quasars because quasars with redshift in this range have similar optical colors as normal stars and are thus difficult to be found in optical sky surveys. A quasar candidate, SDSS J085543.40-001517.7, which was selected by a recently proposed criterion involving near-IR $Y-K$ and optical $g-z$ colors, was identified spectroscopically as a new quasar with redshift of 2.427 by the LAMOST commissioning observation in December 2009 and confirmed by the observation made with the NAOC/Xinglong 2.16m telescope in March 2010. This quasar was not targeted in the SDSS spectroscopic survey because it locates in the stellar locus of the optical color-color diagrams, while it is clearly separated from stars in the $Y-K$ vs. $g-z$ diagram. Comparing with other SDSS quasars we found this new quasar with $i$ magnitude of 16.44 is apparently the brightest one in the redshift range from 2.3 to 2.7. From the spectral properties we derived its central black hole mass as $(1.4\sim3.9) \times 10^{10} M_\odot$ and the bolometric luminosity as $3.7\times 10^{48}$ \ergs, which indicates that this new quasar is intrinsically very bright and belongs to the most luminous quasars in the universe. Our identification supports that quasars in the redshift desert can be found by the quasar selection criterion involving the near-IR colors. More missing quasars are expected to be recovered by the future LAMOST spectroscopic surveys, which is important to the study of the cosmological evolution of quasars at redshift higher than 2.2.

astro-ph.CO↗

arXiv2010

IRAS F13308+5946: A Possible Transition Phase From Type I ULIRG To Optical Quasar

We present a stellar population synthesis study of a type I luminous infrared galaxy (LIRG): IRAS F13308+5946. It is a quasar with absolute magnitude Mi = -22.56 and has a spectral feature of a Seyfert 1.5 galaxy. Optical images show characteristics of later stages of a merger. With the help of the stellar synthesis code STARLIGHT (Cid Fernandes et al. 2005) and both Calzetti et al. (2000) and Leitherer et al.'s (2002) extinction curves, we estimate the past infrared (IR) luminosities of the host galaxy and find it may have experienced an ultraluminous infrared galaxy (ULIRG) phase for nearly 300 Myr, so this galaxy has probably experienced a type I ULIRG phase. Both nuclear starburst and active galactic nuclei (AGN) contribute to the present IR luminosity budget, and starburst contributes ~70%. The mass of supermassive black-hole (SMBH) is M_BH = 1.8*10^8 M_sun and the Eddington ratio L_bol/L_Edd is 0.12, which both approximate to typical values of PG QSOs. These results indicate that IRAS F13308+5946 is probably at the transitional phase from a type I ULIRG to a classical QSO.

astro-ph.CO↗

arXiv2010

Stellar Mass Estimation Based on IRAC Photometry for Spitzer SWIRE-field Galaxies

We analyze the feasibility to estimate the stellar mass of galaxies by mid-infrared luminosities based on a large sample of galaxies cross-identified from $Spitzer$ SWIRE fields and SDSS spectrographic survey. We derived the formulae to calculate the stellar mass by using IRAC 3.6$μ$m and 4.5$μ$m luminosities. The mass-to-luminosity ratios of IRAC 3.6$μ$m and 4.5$μ$m luminosities are more sensitive to star formation history of galaxies than other factors, such as the intrinsic extinction, metallicity and star formation rate. To remove the affection from star formation history, we used g-r color to recalibrate the formulae and obtain a better result. It must be more careful to estimate the stellar mass of low metallicity galaxies using our formulae. Due to the emission from dust heated by hottest young stars, luminous infrared galaxies present higher IRAC 4.5 $μ$m luminosity compared to IRAC 3.6 $μ$m luminosity. For most of type-II AGNs, the nuclear activity can not enhance 3.6$μ$m and 4.5$μ$m luminosities compared with normal galaxies. The star formation in our AGN-hosting galaxies is also very weak, almost all of which are early-type galaxies.

astro-ph.CO↗

arXiv2008

Mid-Infrared Spectroscopic Properties of Ultra-Luminous Infrared Quasars

We analyse mid-infrared (MIR) spectroscopic properties for 19 ultra-luminous infrared quasars (IR QSOs) in the local universe based on the spectra from the Infrared Spectrograph on board the Spitzer Space Telescope. The MIR properties of IR QSOs are compared with those of optically-selected Palomar-Green QSOs (PG QSOs) and ultra-luminous infrared galaxies (ULIRGs). The average MIR spectral features from ~ 5 to 30um, including the spectral slopes, 6.2um PAH emission strengths and [NeII] 12.81um luminosities of IR QSOs, differ from those of PG QSOs. In contrast, IR QSOs and ULIRGs have comparable PAH and [NeII] luminosities. These results are consistent with IR QSOs being at a transitional stage from ULIRGs to classical QSOs. We also find that the colour index alpha(30, 15) is a good indicator of the relative contribution of starbursts to AGNs for all QSOs. Correlations between the [NeII] 12.81um and PAH 6.2um luminosities and those between the [NeII], PAH with 60um luminosities for ULIRGs and IR QSOs indicate that both [NeII] and PAH luminosities are approximate star formation rate indicators for IR QSOs and starburst-dominated galaxies; the scatters are, however, quite large (~ 0.7 to 0.8 dex). Finally the correlation between the EW(PAH 6.2um) and outflow velocities suggests that star formation activities are suppressed by feedback from AGNs and/or supernovae.

astro-ph↗

arXiv2008

Correlations between MIR, FIR, H$α$, and FUV Luminosities for SWIRE galaxies

e present and analyze the correlations between mid-infrared (MIR), far-infrared (FIR), total-infrared (TIR), H$α$, and FUV luminosities for star-forming galaxies, composite galaxies and AGNs, based on a large sample of galaxies selected from the $Spitzer$ SWIRE fields. The MIR luminosities of star-forming galaxies are well correlated with their H$α$, TIR and FUV luminosities, and we re-scaled the MIR-derived SFR formulae according to the above correlations with differences less than 15%. We confirm the recent result by calzetti et al. (2007) that the combined observed H$α$ + 24$μ$m luminosities L(H$α$$_{\rm obs}$+ 24$μ$m) possess very tight correlation with the extinction-corrected H$α$ luminosities L(H$α$$\_$corr) for star-forming and even for dwarf galaxies, and show that the combined L(H$α$$_{\rm obs}$+ 8$μ$m[dust]) are also tightly correlated with L(H$α$$\_$corr) for the above sample galaxies. Among all the L(MIR)-L(FIR) correlations for star-forming galaxies, the L(24$μ$m) vs. L(70$μ$m) and L(8$μ$m[dust]) vs. L(160$μ$m) are the tightest and also nearly linear. The former could be related to young massive star formation, while the latter might be relevant to diffuse dust emissions heated by old stellar populations. Composite galaxies and AGNs have higher MIR-to-H$α$/MIR-to-FUV luminosity ratios than star-forming galaxies, nevertheless their correlations among MIR, FIR and TIR luminosities are completely following those of star-forming galaxies.

astro-ph↗

arXiv2007

Photometric Properties and Scaling Relations of Early Type Brightest Cluster Galaxies

We investigate the photometric properties of the early type Brightest Cluster Galaxies (BCGs) using a carefully selected sample of 85 BCGs from the C4 cluster catalogue with redshift less than 0.1. We perform accurate background subtractions, and surface photometry for these BCGs to 25 $\magsec$ in the Sloan $r$-band. By quantitatively analysing the gradient of the Petrosian profiles of BCGs, we find that a large fraction of BCGs have extended stellar envelopes in their outskirts; more luminous BCGs tend to have more extended stellar halos that are likely connected with mergers. A comparison sample of elliptical galaxies was chosen with similar apparent magnitude and redshift ranges, for which the same photometric analysis procedure is applied. We find that BCGs have steeper size-luminosity ($R \propto L^α$) and Faber-Jackson ($L \propto σ^β$) relations than the bulk of early type galaxies. Furthermore, the power-law indices ($α$ and $β$) in these relations increase as the isophotal limits become deeper. For isophotal limits from 22 to 25 $\magsec$, BCGs are usually larger than the bulk of early type galaxies, and a large fraction ($\sim 49%$) of BCGs have disky isophotal shapes. The differences in the scaling relations are consistent with a scenario where the dynamical structure and formation route of BCGs may be different from the bulk of early type galaxies, in particular dry (dissipationless) mergers may play a more important role in their formation; we highlight several possible dry merger candidates in our sample.

astro-ph↗

arXiv2007

The Effects of Metallicity and AGN Activity on the Mid-Infrared Dust Emission of Galaxies

Using a sample of the $Spitzer$ SWIRE-field galaxies whose optical spectra are taken from the Data Release 4 of the Sloan Digital Sky Survey, we study possible correlations between the Mid-InfraRed (MIR) dust emission from these galaxies and both their metallicities and AGN activities. We find that both metallicity and AGN activity are well correlated with the following ratios: PAH(Polycyclic Aromatic Hydrocarbon)-to-star, VSG(Very Small Grain)-to-star and PAH-to-VSG, which can be characterized by $νL_ν[8μm({\rm dust})]/νL_ν[3.6μm]$, $νL_ν[24μm]/νL_ν[3.6μm]$, and$νL_ν[8μm({\rm dust})]/νL_ν[24μm]$ respectively. We argue that our MIR-metallicity correlation could be explained by either the amount of dust (ongoing dust formation) or dust destruction (PAHs and VSGs could be destroyed by hard and intense radiation fields), and that the MIR-AGN correlation could arise due to either PAH destruction or an enhanced VSG continuum by the central AGN.

astro-ph↗

arXiv2007

Large Misalignment between Stellar Bar and Dust Pattern in NGC 3488 Revealed by Spitzer and SDSS

A large position angle misalignment between the stellar bar and the distribution of dust in the late-type barred spiral NGC 3488 was discovered, using mid-infrared images from the Spitzer Space Telescope and optical images from the Sloan Digital Sky Survey (SDSS). The angle between the bar and dust patterns was measured to be 25+-2deg, larger than most of the misalignments found previously in barred systems based on Ha or HI/CO observations. The stellar bar is bright at optical and 3.6um, while the dust pattern is more prominent in the 8um band but also shows up in the SDSS u and g-band images, suggesting a rich interstellar medium environment harboring ongoing star formation. This angular misalignment is unlikely to have been caused by spontaneous bar formation. We suggest that the stellar bar and the dust pattern may have different formation histories, and that the large misalignment was triggered by a tidal interaction with a small companion. A statistical analysis of a large sample of nearby galaxies with archival Spitzer data indicates that bar structure such as that seen in NGC 3488 is quite rare in the local Universe.

astro-ph↗

arXiv2007

Morphological Dependence of MIR Properties of SDSS Galaxies in the Spitzer SWIRE Survey

We explore the correlation between morphological types and mid-infrared (MIR) properties of an optically flux-limited sample of 154 galaxies from the Forth Data Release (DR4) of Sloan Digital Sky Survey (SDSS), cross-correlated with Spitzer SWIRE (Spitzer Wide-Area InfraRed Extragalactic Survey) fields of ELAIS-N1, ELAIS-N2 and Lockman Hole. Aperture photometry is performed on the SDSS and Spitzer images to obtain optical and MIR properties. The morphological classifications are given based on both visual inspection and bulge-disk decomposition on SDSS g- and r-band images. The average bulge-to-total ratio (B/T) is a smooth function over different morphological types. Both the 8um(dust) and 24um(dust) luminosities and their relative luminosity ratios to 3.6um (MIR dust-to-star ratios) present obvious correlations with both the Hubble T-type and B/T. The early-type galaxies notably differ from the late-types in the MIR properties, especially in the MIR dust-to-star ratios. It is suggested that the MIR dust-to-star ratio is an effective way to separate the early-type galaxies from the late-type ones. Based on the tight correlation between the stellar mass and the 3.6um luminosity, we have derived a formula to calculate the stellar mass from the latter. We have also investigated the MIR properties of both edge-on galaxies and barred galaxies in our sample. Since they present similar MIR properties to the other sample galaxies, they do not influence the MIR properties obtained for the entire sample.

astro-ph↗

arXiv2007

The Growth of Black Holes and Their Host Spheroids in (Sub)mm-loud QSOs at High Redshift

We study the growth of black holes and stellar population in spheroids at high redshift using several (sub)mm-loud QSO samples. Applying the same criteria established in an earlier work, we find that, similar to IR QSOs at low redshift, the far-infrared emission of these (sub)mm-loud QSOs mainly originates from dust heated by starbursts. By combining low-z IR QSOs and high-z (sub)mm-loud QSOs, we find a trend that the star formation rate ($\Mstardot$) increases with the accretion rate ($\Mdot$). We compare the values of $\Mstardot/\Mdot$ for submm emitting galaxies (SMGs), far-infrared ultraluminous/hyperluminous QSOs and typical QSOs, and construct a likely evolution scenario for these objects. The (sub)mm-loud QSO transition phase has both high $\Mdot$ and $\Mstardot$ and hence is important for establishing the correlation between the masses of black holes and spheroids.

astro-ph↗

arXiv2007

Mid-to-Far Infrared Spectral Energy Distribution of Galaxies in Spitzer First Look Survey Field

We made model fitting to the mid-to-far infrared spectral energy distributions (SEDs) for different categories of galaxies in the main extragalactic field of the {\it Spitzer} First Look Survey with the aid of spectroscopic information from the Sloan Digital Sky Survey. We find that the mid-to-far infrared SEDs of HII galaxies, mixture type galaxies and LINERs can be well fitted by the one-parameter ($α$) dust model of Dale et al. plus the 13 Gyr dust-free elliptical galaxy model. The statistics of $α$ values indicates that all these galaxies tend to be quiescent, although the HII galaxies are relatively more active than the LINERs. The mid-infrared SEDs of absorption galaxies are well fitted simply by the 13 Gyr dust-free elliptical galaxy template, and the near-to-mid infrared SEDs of QSOs can be represented by AGN NGC 5506.

astro-ph↗

arXiv2006

Multi-wavelength Study of Young Massive Star Clusters in the Interacting Galaxy ARP 24

We made a multi-wavelength study of young massive star clusters (YSCs) in the interacting galaxy ARP 24, using the optical and ultraviolet images from Hubble Space Telescope (HST), Sloan Digital Sky Survey, and Galaxy Evolution Explorer; the mid-infrared images from Spitzer Space Telescope; and the narrow-band Ha image and optical spectra from the NAOC 2.16m telescope. Based on the HST images, we found that the brightest infrared knot in ARP 24 is associated with a complex of five young massive star clusters, within a region of ~ 0.95" radius (127pc) in size. The ages and masses of the star clusters in this complex and other regions were estimated using HST broadband photometries and the Starburst99 synthesis models. The star clusters in this complex are very young (within ages of ~ 3-5 Myr) and massive (masses of ~ 10^5 Msun). The ionization parameter and metallicity of the complex were estimated using the emission line ratios, and the star formation rates were calculated using monochromatic 24um, FUV, and Ha line luminosities. We speculate that ARP 24 may formed by a retrograde fly-by encounter indicated by its one-armed appearance and fan-like structure, and the formation of the YSCs in this galaxy is triggered by the interaction. The clusters in the YSC complex may formed in a single giant molecular cloud simultaneously. From the ultraviolet to mid-infrared spectral energy distributions, we found that the region of the YSC complex is relatively bluer in optical and has higher 24um dust emission relative to the starlight and 8um emission. This warm infrared color may due to strong UV radiation field or other mechanisms (e.g., shocks) within this region which may destroy the Polycyclic Aromatic Hydrocarbons and enhance the small grain emission at 24um.

astro-ph↗

arXiv2006

Isophotal Shapes of Elliptical/S0 Galaxies from the Sloan Digital Sky Survey

We revisit the shapes of isophotes for elliptical (E) and lenticular (S0) galaxies by studying 847 nearby early-type galaxies selected from the Sloan Digital Sky Survey Data Release 4 with velocity dispersions above 200 km/s. The IRAF task {\tt ellipse} was used to derive the deviations of the isophotes from pure ellipses (Fourier coefficients a_3/a and a_4/a), position angles and ellipticities as a function of radius. We show the statistical distributions of the a_3/a and a_4/a parameters as a function of velocity dispersion, magnitude, and colour. The a_4/a parameter is correlated with the ellipticity and absolute Petrosian magnitude of galaxies. No significant correlation was found between the a_4/a parameter with colour and velocity dispersion. A cross-correlation between the FIRST survey and the SDSS data reveals a lack of powerful radio emitters in discy E/S0s, as previously found by Bender et al. We also find that boxy E/S0s favor denser environments while discy E/S0s favor more isolated environments. The median values of changes in the ellipticity and position angle between one and one and a half Petrosian half-light radii in the isophotes are about -0.023 and 1.61 degree respectively. The average change in the position angle is much larger, about 4.12 degree, due to an extended tail. The change in ellipticity is weakly correlated with the ellipticity itself, with an increasing ellipticity for galaxies with higher ellipticity as the radius increases. The isophote parameters for the 847 galaxies are available online.

astro-ph↗

arXiv2006

Luminous Infrared Galaxies in the Local Universe

We study the morphology and star formation properties of 159 local luminous infrared galaxy (LIRG) using multi-color images from Data Release 2 (DR2) of the Sloan Digital Sky Survey (SDSS). The LIRGs are selected from a cross-correlation analysis between the IRAS survey and SDSS. They are all brighter than 15.9 mag in the r-band and below redshift ~ 0.1, and so can be reliably classified morphologically. We find that the fractions of interacting/merging and spiral galaxies are ~ 48% and ~ 40% respectively. Our results complement and confirm the decline (increase) in the fraction of spiral (interacting/merging) galaxies from z ~1 to z ~ 0.1, as found by Melbourne, Koo & Le Floc'h (2005). About 75% of spiral galaxies in the local LIRGs are barred, indicating that bars may play an important role in triggering star formation rates > 20 M_{sun}/yr in the local universe. Compared with high redshift LIRGs, local LIRGs have lower specific star formation rates, smaller cold gas fractions and a narrower range of stellar masses. Local LIRGs appear to be either merging galaxies forming intermediate mass ellipticals or spiral galaxies undergoing high star formation activities regulated by bars.

astro-ph↗