Differences in the spatial distributions of stars and ionized gas relative to dust in galaxies imply that stellar and nebular dust attenuation curves need not be identical. Although stellar attenuation curves have been extensively studied, nebular attenuation curves remain less explored. In this work, we investigate nebular attenuation curves using Balmer line ratios for a sample of 90,958 nearby star-forming galaxies from the Sloan Digital Sky Survey with well-constrained stellar attenuation curves. In the Hα/Hβ versus Hα/Hγ diagram, the nebular attenuation curves are, on average, significantly shallower than typical stellar attenuation curves, which can be qualitatively reproduced by source-dust geometric effects. The nebular attenuation curve slopes show weak positive correlations with the stellar attenuation curve slopes and weak dependences on galaxy properties that broadly follow those of the stellar attenuation curve slopes. These results suggest that nebular attenuation curves are distinct from stellar attenuation curves, while remaining consistent with a connection between them.

Context. The clustering of dark-matter halos depends primarily on halo mass. However, when using a fixed halo mass, numerical simulations have been able to reveal multiple secondary dependencies. This so-called secondary halo bias has important implications for our understanding of structure formation and observational cosmology. Despite its significance, the effect has not yet been measured observationally with statistical confidence. Aims. We aim to develop the first observational method to probe halo spin bias: the secondary dependence of halo clustering on halo spin at a fixed halo mass. Methods. We used a proxy for halo spin based on the coherent motion of galaxies within and around a halo. We tested this technique using the IllustrisTNG hydrodynamical simulation and subsequently applied it to a group catalog from the Sloan Digital Sky Survey (SDSS). By splitting the SDSS groups according to this spin proxy and measuring the two-point correlation function of the resulting samples, we investigated the existence of halo spin bias. Results. We find consistent indications that at a fixed mass, groups with higher values for the spin proxy exhibit a higher bias than those with lower spin proxy values on scales of 5-15 h(-1) Mpc. The highest significance was observed for groups with halo masses M-h greater than or similar to 10(13.2)h(-1) M-circle dot, for which 85% of the sampled measurements display the expected trend. As we continue to improve on the method, our results could open new avenues for studying the connection between halo spin and the large-scale structure through the use of upcoming spectroscopic surveys.

We present a series of parameter recovery test results of the Bayesian analysis tool IZI, which analyses emission lines from H II regions and star-forming galaxies and returns the estimates of the gas metallicity 12 + log (O/H), ionization parameter log q, and nebular emission-line colour excess E(B-V). We created several mock data sets using IZI to represent a few different ideal or realistic data sets and performed parameter estimation on the mock data with IZI. We found that IZI underestimated or overestimated the parameters by approximately 1 sigma or greater when the model error was included, even when using all emission lines available in the model grids. We strongly recommend that IZI users run parameter recovery tests adjusted for their data before interpreting the IZI estimates. To encourage the appropriate use of IZI, we also share a script for parameter recovery tests. The cause of IZI's biased estimation is the substantial model error in the likelihood term, which varies with the model parameters. We thus note that any parameter estimation with a substantial, varying model error in the likelihood term could return biased estimates for the model parameters, such as in the case of nebulabayes, another Bayesian analysis tool for photoionization emission lines. We also note two issues relevant to setting the log q prior using the observed line ratio [S III] lambda lambda 9068,9532/[S II] lambda 6717, lambda 6731 (the mismatch of line flux terms and violation of Bayes' theorem) and propose a way to avoid the issues.

During cluster assembly, a cluster’s virialization process leaves behind signatures that can provide information on its dynamical state. However, no clear consensus yet exists on the best way to achieve this. Therefore, we attempt to derive improved recipes for classifying the dynamical states of clusters in observations using cosmological simulations. The cluster halo mass and their subhalos’ mass are used to 10 14 M ⊙ h −1 and 10 10 M ⊙ h −1 to calculate five independent dynamical state indicators. We experiment with recipes by combining two to four indicators for detecting specific merger stages, like recent and ancient mergers. These recipes are made by plotting merging clusters and a control sample of relaxed clusters in multiple-indicator parameter space, then applying a rotation matrix method to derive the best way to separate mergers from the control sample. The success of the recipe is quantified using the success rate and overlap percentage of the merger and control histograms along the newly rotated x -axis. This provides us with recipes using different numbers of combined indicators and for different merger stages. Among the recipes, the stellar mass gap and center offset are the first and second most dominant of the indicators, and using more indicators improves the effectiveness of the recipe. When applied to observations, our results show good agreement with literature values of cluster dynamical states.

ABSTRACT Ram pressure stripping is perhaps the most efficient mechanism for removing gas and quenching galaxies in dense environments, as they move through the intergalactic medium. Extreme examples of on-going ram pressure stripping are known as jellyfish galaxies, characterized by a tail of stripped material that can be directly observed in multiple wavelengths. Using the largest homogeneous broad-band optical jellyfish candidate sample in local clusters known to date, we measure the angle between the direction of the tails visible in the galaxies, and the direction towards the host cluster centre. We find that 33 per cent of the galaxy tails point away from the cluster centre, 18 per cent point towards the cluster centre, and 49 per cent point elsewhere. Moreover, we find stronger signatures of ram pressure stripping happening on galaxies with a tail pointing away and towards the cluster centre, and larger velocity dispersion profiles for galaxies with tails pointing away. These results are consistent with a scenario where ram pressure stripping has a stronger effect for galaxies following radial orbits on first infall. The results also suggest that in many cases, radially infalling galaxies are able to retain their tails after pericenter and continue to experience significant on-going ram pressure stripping. We further constrain the lifespan of the optical tails from the moment they first appear to the moment they disappear, by comparing the observed tail directions with matched N-body simulations through Bayesian parameter estimation. We obtain that galaxy tails appear for the first time at $\sim 1.16$R$_{200}$ and disappear $\sim 660$ Myr after pericenter.

In my previous reanalysis of the local star-forming galaxies observed in the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) pilot survey, I reported that the overestimation of E(B - V), hence the star formation rate (SFR), undermined the claim of new galaxy population discovery in the original study. Herein, I re-examine whether the E(B - V) overestimation problem can be alleviated in the Bayesian parameter estimation framework by adopting scientifically motivated new priors. I modelled the emission-line fluxes of galaxies using the strong-line method and four model parameters-metallicity 12 + log (O/H), nebula emission-line colour excess E(B - V), intrinsic [O III] λ5007 line flux and intrinsic [N II] λ6584 line flux. Based on mock-data tests, I found that all input values can be recovered within and around the 1-σ credible interval by adopting suitable priors for the intrinsic [O III] λ5007 and [N II] λ6584 line fluxes: the inverse gamma distribution reflecting the logical constraint that an intrinsic emission-line flux must exceed the observed (reddened) emission-line flux. The mock-data tests were performed for two metallicity calibrations, three colour excess input values [E(B - V) = 0.1, 0.3 and 0.5] and two metallicity input values [12 + log (O/H) = 8.0 and 8.5]. I also found that the new prior can diminish the SFR overestimation eightfold. This study demonstrates how the Bayesian parameter estimation can achieve more accurate estimates with no further observations when the likelihood does not constrain the model parameters correctly.

We present a new approach for observationally constraining where the tails of Jellyfish (JF) galaxies in groups and clusters first appear and how long they remain visible for with respect to the moment of their orbital pericenter. This is accomplished by measuring the distribution of their tail directions, with respect to their host centers, and their distribution in a projected velocity–radius phase-space diagram. We then model these observed distributions using a fast and flexible approach, where JF tails are painted onto dark matter halos, according to a simple parameterized prescription, before a Bayesian analysis is performed to estimate the parameters. We demonstrate the effectiveness of our approach using observational mocks, then apply it to a known observational sample of 106 JF galaxies, with radio-continuum tails located inside 68 hosts such as groups and clusters. We find that, typically, the radio-continuum tails become visible on first infall, when the galaxy reaches roughly three-quarters of r 200 , and the tails remain visible for a few hundred Myr after pericenter passage. Lower-mass galaxies in more massive hosts tend to form visible tails further out and their tails disappear more quickly after pericenter. We argue that this indicates that they are more sensitive to ram pressure stripping. With upcoming large-area surveys of JF galaxies in progress, this is a promising new method for constraining the environmental conditions in which visible JF tails exist.

ABSTRACT I have reanalysed the data obtained for local (z < 0.15) star-forming galaxies during the pilot survey for the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX) – called the HETDEX Pilot Survey (HPS) – which uses an integral-field-unit spectrograph and covers ∼3500−5800 Å at ∼5-Å resolution. I have newly determined the gas metallicities, $12 + \text{log (O/H)}$, following the Bayesian analysis scheme of the previous study, but dealing carefully with the uncertainty of strong-line calibration, performing reproducibility tests with mock data, and monitoring the convergence of the Markov chain Monte Carlo (MCMC) sampling. From the mock-data tests, I found that the nebular emission-line colour excess E(B − V) can be overestimated by as much as 2σ or more, although the metallicity can recover the input value to within 1σ. The new metallicity estimates on the HPS data are from well-converged MCMC samples (effective sample sizes > 2000), and they are higher than the previous estimates by ∼2σ. Using the HPS data, I also showed that the MCMC sampling can have the statistical accuracy as poor as the one near the iteration start if done without convergence monitoring. The overestimation of E(B − V) indicates the overestimation of the star formation rates (SFRs) in the previous study, which can be as much as a factor of 5. This finding undermines the previous suggestion of a hitherto-unknown galaxy population based on the locations of galaxies in the mass–SFR plane. I found that the independent determination of E(B − V) using either H β-H γ or H α-H β line pair is ideal for the analysis of forthcoming HETDEX data, but it requires additional cost.

We have revisited the target EON_10.477_41.954 in order to determine more accurately the uncertainties in the model parameters that are important for target classification (i.e. galaxies with or without substantial extraplanar dust). We performed a Markov chain Monte Carlo (MCMC) analysis for the 15 parameters of the three-dimensional radiative-transfer galaxy model we used previously for target classification. To investigate the convergence of the MCMC sampling – which is usually neglected in the literature but should not be – we monitored the integrated autocorrelation time (τint), and we achieved effective sample sizes >5650 for all the model parameters. The confidence intervals are unstable at the beginning of the iterations where the values of τint are increasing, but they become stable in later iterations where those values are almost constant. The final confidence intervals are ∼5–100 times larger than the nominal uncertainties used in our previous study (the standard deviation of three best-fitting results). Thus, those nominal uncertainties are not good proxies for the model-parameter uncertainties. Although the position of EON_10.477_41.954 in the target-classification plot (the scale height to diameter ratio of dust versus that of light source) decreases by about 20–30 per cent when compared to our previous study, its membership in the ‘high-group’ – i.e. among galaxies with substantial extraplanar dust – nevertheless remains unchanged.

We present a list of edge-on galaxies that might have substantial extraplanar dust. Twenty-three edge-on galaxies were selected as target galaxies from an edge-on galaxy catalog, and their Galaxy Evolution Explorer far-ultraviolet images were fitted with a three-dimensional radiative transfer galaxy model. The galaxy model is described by two disks: one for the light source and the other for the dust. The best-fit parameters were found by employing a global optimization method called differential evolution. To find the galaxies with substantial extraplanar dust using the best-fit parameters, we plotted the ratio of scale height to galactic diameter: zs/D25,ph (light source) versus zd/D25,ph (dust). We found that 17 and 6 galaxies fall on the region of (zs/D25,ph × 100) >0.2 and (zs/D25,ph × 100) < 0.2, respectively. The former is labeled "high-group" and the latter is labeled "low-group." We conclude that "high-group" galaxies likely have substantial extraplanar dust, while "low-group" galaxies likely have little extraplanar dust, i.e., typical galactic thin disks, based on the following points: (1) the relative positions of "high-group" and "low-group" on the plot zs/D25,ph versus zd/D25,ph with respect to the reference values from optical radiative transfer studies; (2) the lower scale height of the young stellar population than the old stellar population; and (3) a test result that shows the existence of extraplanar dust causes zs and zd to be overestimated in the fitting results. We also examined the dependence of the group separation on the surface density of far-ultraviolet luminosity (), but found no strong dependence.

We compare vertical profiles of the extraplanar Hα emission to those of the UV emission for 38 nearby edge-on late-type galaxies. It is found that detection of the “diffuse” extraplanar dust (eDust), traced by the vertically extended, scattered UV starlight, always coincides with the presence of the extraplanar Hα emission. A strong correlation between the scale heights of the extraplanar Hα and UV emissions is also found; the scale height at Hα is found to be ∼0.74 of the scale height at FUV. Our results may indicate the multiphase nature of the diffuse ionized gas and dust in the galactic halos. The existence of eDust in galaxies where the extraplanar Hα emission is detected suggests that a larger portion of the extraplanar Hα emission than that predicted in previous studies may be caused by Hα photons that originate from H ii regions in the galactic plane and are subsequently scattered by the eDust. This possibility raise an advantage in studying the extraplanar diffuse ionized gas. We also find that the scale heights of the extraplanar emissions normalized to the galaxy size correlate well with the star formation rate surface density of the galaxies. The properties of eDust in our galaxies is on a continuation line of that found through previous observations of the extraplanar polycyclic aromatic hydrocarbons emission in more active galaxies known to have galactic winds.

In order to examine their relation to the host galaxy, the extraplanar dusts of six nearby galaxies are modeled, employing a three-dimensional Monte Carlo radiative transfer code. The targets are from the highly inclined galaxies that show dust-scattered ultraviolet halos, and the archival Galaxy Evolution Explorer FUV band images were fitted with the model. The observed images are generally well-reproduced by two dust layers and one light source layer, whose vertical and radial distributions have exponential profiles. We obtained several important physical parameters, such as star formation rate (SFRUV), face-on optical depth, and scale-heights. Three galaxies (NGC 891, NGC 3628, and UGC 11794) show clear evidence for the existence of an extraplanar dust layer. However, it is found that the remaining three targets (IC 5249, NGC 24, and NGC 4173) do not necessarily need a thick dust disk to model the ultraviolet (UV) halo, because its contribution is too small and the UV halo may be caused by the wing part of the GALEX point spread function. This indicates that the galaxy samples reported to have UV halos may be contaminated by galaxies with negligible extraplanar (halo) dust. The galaxies showing evidence of an extraplanar dust layer fall within a narrow range on the scatter plots between physical parameters such as SFRUV and extraplanar dust mass. Several mechanisms that could possibly produce the extraplanar dust are discussed. We also found a hint that the extraplanar dust scale-height might not be much different from the polycyclic aromatic hydrocarbon emission characteristic height.

We report the detection of vertically extended far-ultraviolet and near-UV emissions in an edge-on spiral galaxy NGC 891, which we interpret as being due to dust-scattered starlight. Three-dimensional radiative transfer models are used to investigate the content of the extraplanar dust that is required to explain the UV emission. The UV halos are well reproduced by a radiative transfer model with two exponential dust disks, one with a scale height of approximate to 0.2-0.25 kpc and the other with a scale height of approximate to 1.2-2.0 kpc. The central face-on optical depth of the geometrically thick disk is found to be tau(thick)(B) approximate to 0.3-0.5 at the B band. The results indicate that the dust mass at vertical bar z vertical bar > 2 kpc is approximate to 3%-5% of the total dust mass, which is in good accordance with the recent Herschel submillimeter observation. Our results, together with the recent discovery of the UV halos in other edge-on galaxies, suggest the widespread existence of a geometrically thick dust layer above the galactic plane in spirals.

We present [Fe II] 1.644 mu m features around ultracompact H II regions (UCHIIs) found on a quest for the "footprint" outflow features of UCHIIs-the features produced by outflowing materials ejected during an earlier, active accretion phase of massive young stellar objects (MYSOs). We surveyed 237 UCHIIs in the first Galactic quadrant, employing the CORNISH UCHII catalog and UWIFE data, which is an imaging survey in [Fe II] 1.644 mu m performed with UKIRT-WFCAM under similar to 0 ''.8 seeing conditions. The [Fe II] features were found around five UCHIIs, one of which was less plausible. We interpret the [Fe II] features to be shock-excited by outflows from YSOs and estimate the outflow mass-loss rates from the [Fe II] flux which are similar to 1 x 10(-6)-4 x 10(-5) M-circle dot yr(-1). We propose that the [Fe II] features might be the "footprint" outflow features, but more studies are required to clarify whether or not this is the case. This is based on the morphological relation between the [Fe II] and 5 GHz radio features, the outflow mass-loss rate, the travel time of the [Fe II] features, and the existence of several YSO candidates near the UCHIIs. The UCHIIs accompanying the [Fe II] features have relatively higher peak flux densities. The fraction of UCHIIs accompanying the [Fe II] features, 5/237, is small when compared to the similar to 90% detection rate of high-velocity CO gas around UCHIIs. We discuss some possible explanations for the low detection rate.

The United Kingdom Infrared Telescope (UKIRT) Widefield Infrared Survey for Fe+ (UWIFE) is a 180 deg(2) imaging survey of the first Galactic quadrant (7 degrees < l < 62 degrees; |b| less than or similar to 1 degrees.5) that uses a narrow-band filter centred on the [Fe II] 1.644-mu m emission line. The [Fe II] 1.644-mu m emission is a good tracer of dense, shock-excited gas, and the survey will probe violent environments around stars: star-forming regions, evolved stars, and supernova remnants, among others. The UWIFE survey is designed to complement the existing UKIRT Widefield Infrared Survey for H-2 (UWISH2). The survey will also complement existing broad-band surveys. The observed images have a nominal 5 sigma detection limit of 18.7 mag for point sources, with a median seeing of 0.83 arcsec. For extended sources, we estimate a surface brightness limit of 8.1 x 10(-20) W m(-2) arcsec(-2). In this paper, we present an overview and some preliminary results of this survey.

We present [Fe II] 1.64 mu m imaging observations for jets and outflows from young stellar objects (YSOs) over the northern part (similar to 24' x 45') of the Carina Nebula, a massive star-forming region. The observations were performed with IRIS2 of the Anglo-Australian Telescope and the seeing was similar to 1 ''.5 +/- 0 ''.5. Eleven jet and outflow features are detected at eight different regions and are termed ionized Fe objects (IFOs). One Herbig-Haro candidate that was missed in Hubble Space Telescope H alpha observations is newly identified as HHc-16, referring to our [Fe II] images. IFOs have knotty or longish shapes, and the detection rate of IFOs against previously identified YSOs is 1.4%, which should be treated as a lower limit. Four IFOs show anti-correlated peak intensities in [Fe II] and H alpha, where the ratio I([Fe II])/I(H alpha) is higher for longish IFOs than for knotty IFOs. We estimate the outflow mass loss rate from the [Fe II] flux using two different methods. The jet-driving objects are identified for three IFOs (IFO-2, -4, and -7) for which we study the relations between the outflow mass loss rate and the YSO physical parameters from the radiative transfer model fitting. The ratios of the outflow mass loss rate over the disk accretion rate for IFO-4 and -7 are consistent with the previously reported values (10(-2)-10(+1)), while the ratio is higher for IFO-2. This excess may result from underestimating the disk accretion rate. The jet-driving objects are likely to be low-or intermediate-mass stars. Other YSO physical parameters, such as luminosity and age, show reasonable relations or trends.