The gas-to-dust ratio of reddened stars in the Milky Way (MW), the Magellanic Clouds, and in general, is usually expressed as a linear relation between the hydrogen column density, N(H), and the ...reddening, E(B − V), or extinction in the V-band (A V ). If the extinction curve were truly universal, the strength of the relationship and the linearity would naturally be maintained for extinction at any wavelength, as well as for N(H) versus E(B − V). However, extinction curves vary within the MW, and there is no reason, except by chance, why either E(B − V) or A V would be the most physical measure of dust column density. In this paper, we utilize for the first time full extinction curves to 41 MW sightlines, finding that the scatter between N(H) and extinction is minimized—and the relation becomes linear—for extinction at 2900 ± 160 Å. Scatter and nonlinearity increase at longer wavelengths, and are especially large for near-IR extinction. We conclude that near-UV extinction is a superior measure of the dust column density for MW dust. We provide new, nonlinear gas-to-dust relations for various dust tracers. We also find that the very large discrepancy between MW and SMC gas-to-dust ratios of 0.9 dex in N(H)/E(B − V) is reduced to 0.7 dex for far-UV extinction, which matches the difference in cosmic abundances of carbon between the two galaxies, and therefore confirms that N(C) is the preferred measure for gas in the gas-to-dust ratio, even though it may not be a convenient one.
We introduce the Mass-Excitation (MEx) diagnostic to identify active galactic nuclei (AGNs) in galaxies at intermediate redshift. In the absence of near-infrared spectroscopy, necessary for using ...traditional nebular line diagrams at z > 0.4, we demonstrate that combining O III Delta *l5007/H Delta *b and stellar mass successfully distinguishes between star formation and AGN emission. The MEx classification scheme relies on a novel probabilistic approach splitting galaxies into sub-categories with more confidence than alternative high-z diagnostic diagrams. It recognizes that galaxies near empirical boundaries on traditional diagrams have an uncertain classification and thus a non-zero probability of belonging to more than one category. An outcome of this work is a system of statistical weights that can be used to compute global properties of galaxy samples. We apply the MEx diagram to 2812 galaxies at 0.3 < z < 1 in the Great Observatories Origins Deep Survey North and Extended Groth Strip fields, and compare it to an independent X-ray classification scheme. We identify Compton-thick AGN candidates with large X-ray absorption, which we infer from the luminosity ratio between hard X-ray emission and O III Delta *l5007, a nearly isotropic tracer of AGNs. X-ray stacking of sources that were not detected individually supports the validity of the MEx diagram and yields a very flat spectral slope for the Compton-thick candidates ( Delta *G 0.4; unambiguously indicating absorbed AGNs). We present evidence that composite galaxies, which are difficult to identify with alternative high-redshift diagrams, host the majority of the highly absorbed AGNs. Our findings suggest that the interstellar medium of the host galaxy provides significant absorption in addition to the torus invoked in AGN unified models.
This study explored the nematicidal activity of silver nanoparticles (AgNPs), ascorbic (AA) and salicylic acid (SA) compared with Mycorrihizin (Myco) against Meloidogyne javanica infecting eggplants. ...The characterization and size confirmation of the AgNPs was done by ultraviolet-visual (UV-vis) spectrophotometry, surface zeta-potential and transmission electron microscopy. The results illustrated that 150 μg/mL AgNPs had nematicidal activity against the second-stage juvenile and egg hatching of M. javanica in vitro, and caused 100% mortality in juveniles after 48 h of exposure. In open-field conditions, the treatment with 100 µg and 150 µg AgNPs 24 h before transplanting killed almost all of the nematode eggs and galls per root system compared with the control. All treatments improved the eggplant growth in terms of plant height, root weight, number and weight of fruits, shoot and root length and fresh weight of shoot and root with various degrees as compared to control. The activities of oxidative enzymes, peroxidase (POX), polyphenol oxidase (PPO) and phenylalanine ammonia lyase (PAL), during the flowering stage, increased with all treatments comparing to healthy and infected plants. To assess the defense response of infected eggpant, the gene expression levels (PAL, POX and PPO) were monitored using quantitative reverse transcription polymerase chain reaction (qRT-PCR). The PPO enzyme showed the highest rate on day 60 after infection when 50 µg AgNPs were used during transplanting. The POX enzyme activity showed the highest increase in all treatments during all stages of growth, on day 30, 45 and 60.
ABSTRACT Recent studies have shown that the local mass-metallicity (M*-Z) relation depends on the specific star formation rate (sSFR). Whether such a dependence exists at higher redshifts, and ...whether the resulting M*-Z-SFR relation is redshift invariant, is debated. We re-examine these issues by applying the non-parametric techniques of Salim et al. to ∼130 galaxies with N2 and O3 measurements from Keck Baryonic Structure Survey (KBSS). We find that the KBSS M*-Z relation depends on sSFR at intermediate masses where such dependence exists locally. KBSS and SDSS galaxies of the same mass and sSFR ("local analogs") are similarly offset in the BPT diagram relative to the bulk of local star-forming galaxies, and thus we posit that metallicities can be compared self-consistently at different redshifts as long as the masses and sSFRs of the galaxies are similar. We find that the M*-Z-SFR relation of galaxies is consistent with the local one at , but is offset up to −0.25 dex at higher masses, so it is altogether not redshift invariant. This high-mass offset could arise from a bias that O iii-based, high-redshift spectroscopic surveys have against high-metallicity galaxies, but additional evidence disfavors this possibility. We identify three causes for the reported discrepancy between N2 and O3N2 metallicities at : (1) a smaller offset that is also present for SDSS galaxies, which we remove with new N2 calibration, (2) a genuine offset due to differing ISM condition, which is also present in local analogs, and (3) an additional offset due to unrecognized active galactic nucleus contamination.
ABSTRACT
K-corrections – a necessary ingredient for converting between flux in observed bands to flux in rest-frame bands – are critical for comparing galaxies at differing redshifts. These ...corrections often rely on fits to empirical or theoretical spectral energy distribution (SED) templates of galaxies. However, templates can only produce reliable K-corrections in regimes where SED models are robust. For instance, the templates utilized in some popular software packages are not well-constrained in some bands (e.g. WISE W4 in Kcorrect), which results in ill-behaved K-corrections. We address this shortcoming by developing an empirically driven approach to K-corrections that limits the dependence on SED templates. We perform a polynomial fit for the K-correction as a function of a galaxy’s rest-frame colour determined in a pair of well-constrained bands (e.g. 0(g − r)) and redshift, exploiting the fact that galaxy SEDs can be approximated as a one-parameter family at low redshift. For bands well-constrained by SED templates, our empirically driven K-corrections yield results comparable to the SED fitting methods used by Kcorrect and the GSWLC-M2 catalogue (the updated medium-deep GALEX–SDSS–WISE Legacy Catalogue). However, our method dramatically outperforms Kcorrect derived K-corrections for WISE W4. Our method is also robust to incorrect template assumptions outside of the optical bands and enforces that the K-correction must be zero at z = 0. Our K-corrected photometry and code are publicly available.
Ultraviolet-luminous galaxies (UVLGs) have been identified as intensely star-forming nearby galaxies. A subset of these, the supercompact UVLGs, are believed to be local analogs of high-redshift ...Lyman break galaxies. Here we investigate the radio continuum properties of this important population for the first time. We have observed 42 supercompact UVLGs with the VLA, all of which have extensive coverage in the UV/optical by GALEX and SDSS. Our analysis includes comparison samples of multiwavelength data from the Spitzer First Look Survey and from the SDSS-GALEX matched catalogs. In addition we have Spitzer MIPS data for 24 of our galaxies and find that they fall on the radio-FIR correlation of normal star-forming galaxies. We find that our galaxies have lower radio to UV ratios and lower Balmer decrements than other local galaxies with similar (high) star formation rates. Optical spectra show they have lower unk(4000) and H delta sub(A) indices, higher H beta emission-line equivalent widths, and higher O III5007/H beta emission-line ratios than normal star-forming galaxies. Comparing these results to galaxy spectral evolution models we conclude that supercompact UVLGs are distinguished from normal star-forming galaxies firstly by their high specific star formation rates. Moreover, compared to other types of galaxies with similar star formation rates, they have significantly less dust attenuation. In both regards they are similar to Lyman break galaxies. This suggests that the process that causes star formation in the supercompact UVLGs differs from other local star-forming galaxies, but may be similar to Lyman break galaxies.
In recent years, an argument has been made that a high fraction of early-type galaxies (ETGs) in the local universe experience low levels ({approx_lt}1 M {sub sun} yr{sup -1}) of star formation (SF) ...that causes strong excess in UV flux, yet leaves the optical colors red. Many of these studies were based on Galaxy Evolution Explorer imaging of Sloan Digital Sky Survey (SDSS) galaxies (z {approx} 0.1), and were thus limited by its 5'' FWHM. Poor UV resolution left other possibilities for UV excess open, such as the old populations or an active galactic nucleus (AGN). Here, we study high-resolution far-ultraviolet HST/ACS images of optically quiescent early-type galaxies with strong UV excess. The new images show that three-quarters of these moderately massive ({approx}5 x 10{sup 10} M {sub sun}) ETGs shows clear evidence of extended SF, usually in form of wide or concentric UV rings, and in some cases, striking spiral arms. SDSS spectra probably miss these features due to small fiber size. UV-excess ETGs have on average less dust and larger UV sizes (D > 40 kpc) than other green-valley galaxies, which argues for an external origin for the gas that is driving the SF. Thus, most of these galaxies appear 'rejuvenated' (e.g., through minor gas-rich mergers or intergalactic medium accretion). For a smaller subset of the sample, the declining SF (from the original internal gas) cannot be ruled out. SF is rare in very massive early-types (M {sub *} > 10{sup 11} M {sub sun}), a possible consequence of AGN feedback. In addition to extended UV emission, many galaxies show a compact central source, which may be a weak, optically inconspicuous AGN.
ABSTRACT Major mergers between galaxies are predicted to fuel their central supermassive black holes (SMBHs), particularly after coalescence. However, determining the prevalence of active galactic ...nuclei (AGNs) in mergers remains a challenge, because AGN diagnostics are sensitive to details of the central structure (e.g. nuclear gas clouds, geometry, and orientation of a dusty torus) that are partly decoupled from SMBH accretion. X-rays, expected to be ubiquitous among accreting systems, are detectable through non-Compton-thick screens of obscuring material, and thus offer the potential for a more complete assessment of AGNs in mergers. But extant statistical X-ray studies of AGNs in mergers have been limited by either sparse, heterogeneous, or shallow on-sky coverage. We use new X-ray observations from the first SRG/eROSITA all-sky data release to characterize the incidence, luminosity, and observability of AGNs in mergers. Combining machine learning and visual classification, we identify 923 post-mergers in Dark Energy Camera Legacy Survey (DECaLS) imaging and select 4565 interacting galaxy pairs (with separations <120 kpc and mass ratios within 1:10) from the Sloan Digital Sky Survey. We find that galaxies with X-ray AGNs are 2.0$\pm$0.24 times as likely to be identified as post-mergers compared to non-AGN controls, and that post-mergers are 1.8$\pm$0.1 times as likely to host an X-ray AGN as non-interacting controls. A multiwavelength census of X-ray, optical, and mid-IR-selected AGNs suggests a picture wherein the underlying AGN fraction increases during pair-phase interactions, that galaxy pairs within ~20 kpc become heavily obscured, and that the obscuration often clears post-coalescence.
ABSTRACT
Despite powerful X-ray emission, some active galactic nuclei (AGNs) are known to either lack optical emission lines (so-called ‘optically dull’ AGNs) or have lines that fall on the ...star-forming branch of the Baldwin–Phillips–Terlevich (BPT) diagram (‘misclassified’ AGNs). Aperture effects have been proposed to explain such atypical spectra, especially when based on Sloan Digital Sky Survey (SDSS; 3 arcsec) fibres. We use observations from VLT-MUSE with Adaptive Optics to explore the spatially resolved optical emission line properties of four optically dull and one misclassified X-ray AGN candidates. VLT-MUSE IFU spectra allow us to investigate the extent to which the aperture size affects the emission line measurements. The optically dull AGNs become detectable in deeper VLT-MUSE spectroscopic apertures having the same size (3 arcsec) as SDSS fibres, suggesting no AGN is truly lineless. However, in no case does the line become more detectable as the aperture decreases, as would be expected if dilution by strong continuum was responsible for making the lines appear weak. We also show that the misclassified X-ray AGN retains the same position on the BPT diagram in smaller apertures (down to 0.5 arcsec), demonstrating that its misclassification is not the result of the dilution by H ii regions. Thus, we conclude that continuum swamping or star formation dilution, i.e. aperture effects, are not responsible for atypical lines. Rather, the AGN lines are intrinsically weak.
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