A fundamental assumption adopted in nearly every extragalactic emission-line study is that the attenuation of different emission lines can be described by a single attenuation curve. Here we show ...this assumption fails in many cases with important implications for derived results. We developed a new method to measure the differential nebular attenuation among three kinds of transitions: the Balmer lines of hydrogen, high-ionization transitions, and low-ionization transitions. This method bins the observed data in a multidimensional space spanned by attenuation-insensitive line ratios. Within each small bin, the variations in line ratios are mainly driven by the variations in the nebular attenuation. This allows us to measure the nebular attenuation using both forbidden lines and Balmer lines. We applied this method to a sample of 2.4 million star-forming spaxels from SDSS-IV MaNGA. We found that the attenuation of high ionization lines and Balmer lines can be well described by a single Fitzpatrick (1999) extinction curve with \(R_V=3.1\). However, no single attenuation curve can simultaneously account for all three transitions. This strongly suggests that different lines have different effective attenuations, likely because spectroscopy at kiloparsec resolutions mixes multiple regions with different intrinsic line ratios and different levels of attenuation. As a result, the assumption that different lines follow the same attenuation curve breaks down. Using a single attenuation curve determined by Balmer lines to correct attenuation-sensitive forbidden line ratios could bias the nebular parameters derived by 0.06--0.25 dex at \(A_V = 1\), depending on the details of the dust attenuation model. Observations of a statistically large sample of H II regions with high spatial resolutions and large spectral coverage are vital for improved modeling and deriving accurate corrections for this effect.
We present the identification of 42 narrow-line active galactic nuclei (type-2 AGN) candidates in the two deepest observations of the JADES spectroscopic survey with JWST/NIRSpec. The spectral ...coverage and the depth of our observations allow us to select narrow-line AGNs based on both rest-frame optical and UV emission lines up to z=10. Due to the metallicity decrease of galaxies, at \(z>3\) the standard optical diagnostic diagrams (N2-BPT or S2-VO87) become unable to distinguish many AGN from other sources of photoionisation. Therefore, we also use high ionisation lines, such as HeII\(\lambda\)4686, HeII\(\lambda\)1640, NeIV\(\lambda\)2422, NeV\(\lambda\)3420, and NV\(\lambda\)1240, also in combination with other UV transitions, to trace the presence of AGN. Out of a parent sample of 209 galaxies, we identify 42 type-2 AGN (although 10 of them are tentative), giving a fraction of galaxies in JADES hosting type-2 AGN of about \(20\pm3\)\%, which does not evolve significantly in the redshift range between 2 and 10. The selected type-2 AGN have estimated bolometric luminosities of \(10^{41.3-44.9}\) erg s\(^{-1}\) and host-galaxy stellar masses of \(10^{7.2-9.3}\) M\(_{\odot}\). The star formation rates of the selected AGN host galaxies are consistent with those of the star-forming main sequence. The AGN host galaxies at z=4-6 contribute \(\sim\)8-30 \% to the UV luminosity function, slightly increasing with UV luminosity.
We use the statistical power of the MaNGA integral-field spectroscopic galaxy survey to improve the definition of strong line diagnostic boundaries used to classify gas ionization properties in ...galaxies. We detect line emission from 3.6 million spaxels distributed across 7400 individual galaxies spanning a wide range of stellar masses, star formation rates, and morphological types, and find that the gas-phase velocity dispersion sigma_HAlpha correlates strongly with traditional optical emission line ratios such as S II/HAlpha, N II/HAlpha, O I/HAlpha, and O III/HBeta. Spaxels whose line ratios are most consistent with ionization by galactic HII regions exhibit a narrow range of dynamically cold line of sight velocity distributions (LOSVDs) peaked around 25 km/s corresponding to a galactic thin disk, while those consistent with ionization by active galactic nuclei (AGN) and low-ionization emission-line regions (LI(N)ERs) have significantly broader LOSVDs extending to 200 km/s. Star-forming, AGN, and LI(N)ER regions are additionally well separated from each other in terms of their stellar velocity dispersion, stellar population age, HAlpha equivalent width, and typical radius within a given galaxy. We use our observations to revise the traditional emission line diagnostic classifications so that they reliably identify distinct dynamical samples both in two-dimensional representations of the diagnostic line ratio space and in a multi-dimensional space that accounts for the complex folding of the star forming model surface. By comparing the MaNGA observations to the SDSS single-fiber galaxy sample we note that the latter is systematically biased against young, low metallicity star-forming regions that lie outside of the 3 arcsec fiber footprint.
We present the third data release of JADES, the JWST Advanced Deep Extragalactic Survey, providing both imaging and spectroscopy in the two GOODS fields. Spectroscopy consists of medium-depth and ...deep NIRSpec/MSA spectra of 4,000 targets, covering the spectral range 0.6-5.3 \(\mu\)m and observed with both the low-dispersion prism (R=30-300) and all three medium-resolution gratings (R=500-1,500). We describe the observations, data reduction, sample selection, and target allocation. We measured 2,375 redshifts (2,053 from multiple emission lines); our targets span the range from z=0.5 up to z=13, including 404 at z>5. The data release includes 2-d and 1-d fully reduced spectra, with slit-loss corrections and background subtraction optimized for point sources. We also provide redshifts and S/N>5 emission-line flux catalogs for the prism and grating spectra, and concise guidelines on how to use these data products. Alongside spectroscopy, we are also publishing fully calibrated NIRCam imaging, which enables studying the JADES sample with the combined power of imaging and spectroscopy. Together, these data provide the largest statistical sample to date to characterize the properties of galaxy populations in the first billion years after the Big Bang.
H$\alpha$ blobs are off-galaxy emission-line regions with weak or no optical
counterparts. They are mostly visible in H$\alpha$ line, appearing as
concentrated blobs. Such unusual objects have been ...rarely observed and studied,
and their physical origin is still unclear. We have identified 13 H$\alpha$
blobs in the public data of MaNGA survey, by visually inspecting both the
optical images and the spatially resolved maps of H$\alpha$ line for $\sim
4600$ galaxy systems. Among the 13 H$\alpha$ blobs, 2 were reported in
previously MaNGA-based studies and 11 are newly discovered. This sample, though
still small in size, is by far the largest sample with both deep imaging and
integral field spectroscopy. Therefore, for the first time we are able to
perform statistical studies to investigate the physical origin of H$\alpha$
blobs. We examine the physical properties of these H$\alpha$ blobs and their
associated galaxies, including their morphology, environments, gas-phase
metallicity, kinematics of ionized gas, and ionizing sources. We find that the
H$\alpha$ blobs in our sample can be broadly divided into two groups. One is
associated with interacting/merging galaxy systems, of which the ionization is
dominated by shocks or diffuse ionized gas. It is likely that these H$\alpha$
blobs used to be part of their nearby galaxies, but were stripped away at some
point due to tidal interactions. The other group is found in gas-rich systems,
appearing as low-metallicity star-forming regions that are visually detached
from the main galaxy. These H$\alpha$ blobs could be associated with faint
disks, spiral arms, or dwarf galaxies.
Using integral field spectroscopy from MaNGA, we study the resolved microstructures in a shocked region in Criss Cross Nebula (CCN), with an unprecedentedly high resolution of \(\lesssim\)1000 AU. We ...measure surface brightness maps for 34 emission lines, which can be broadly divided into three categories: (1) the OIII \(\lambda\)5007-like group including seven high-ionization lines and two OII auroral lines which uniformly present a remarkable lane structure, (2) the H\(\alpha\) \(\lambda\)6563-like group including 23 low-ionization or recombination lines which present a clump-like structure, and (3) OII \(\lambda\)3726 and OII \(\lambda\)3729 showing high densities at both the OIII \(\lambda\)5007 lane and the H\(\alpha\) clump. We use these measurements to constrain resolved shock models implemented in MAPPINGS V. We find our data can be reasonably well-fitted by a model which includes a plane-parallel shock with a velocity of \(133\pm5\) km/s, plus an isotropic two-dimensional Gaussian component which is likely another clump of gas ionized by photons from the shocked region, and a constant background. We compare the electron density and temperature profiles as predicted by our model with those calculated using observed emission line ratios. We find different line ratios to provide inconsistent temperature maps, and the discrepancies can be attributed to observational effects caused by limited spatial resolution and projection of the shock geometry, as well as contamination of the additional Gaussian component. Implications on shock properties and perspectives on future IFS-based studies of CCN are discussed.
We report the chemical abundance pattern of GS\_3073, a galaxy at \(z=5.55\) which was previously confirmed to host an overmassive active black hole, by leveraging the detection of about 40 emission ...lines, combining JWST/NIRSpec observations and ground-based (VLT/VIMOS) data. By using rest-frame UV emission lines, which trace high-density (\(\sim 10^5~{\rm cm}^{-3}\)) and highly ionized gas, we derived an abundance ratio of \(\rm log(N/O) = 0.46^{+0.12}_{-0.09}\). At an estimated metallicity of \(0.2~Z_{\odot}\), this is the most extreme nitrogen-rich object found by JWST thus far. In comparison, the relative carbon abundance derived from the rest-frame UV emission lines is \(\rm log(C/O) = -0.30^{+0.12}_{-0.09}\), which is not significantly higher than those in local galaxies and stars with similar metallicities. We also detected coronal lines, including FeVII\(\lambda 6087\) and potentially FeXIV\(\lambda 5303\). We inferred a high Fe abundance of \(\rm Fe/O \gtrsim 0.1\). Overall, the chemical abundance pattern of GS\_3073 is compatible with enrichment by super-massive stars with \(M_* \gtrsim 1000~M_\odot\), ejecta from asymptotic giant branch (AGB) stars, or winds from Wolf-Rayet (WR) stars, although the WR scenario is less likely. Interestingly, when using optical emission lines which trace lower density (\(\sim 10^3~{\rm cm}^{-3}\)) and lower ionization gas, we found a sub-solar N/O ratio. We interpret the difference in N/O derived from UV lines and optical lines as evidence for a stratified system, where the inner and denser region is both more chemically enriched and more ionized. Taking this luminous, well-studied system as a benchmark, our results suggest that nitrogen loudness in high-\(z\) galaxies is confined to the central, dense, and highly ionized region of the galaxy, while the bulk of the galaxy evolves more normally.
SDSS-IV MaNGA (Mapping Nearby Galaxies at Apache Point Observatory) is the largest integral-field spectroscopy survey to date, aiming to observe a statistically representative sample of 10,000 ...low-redshift galaxies. In this paper we study the reliability of the emission-line fluxes and kinematic properties derived by the MaNGA Data Analysis Pipeline (DAP). We describe the algorithmic choices made in the DAP with regards to measuring emission-line properties, and the effect of our adopted strategy of simultaneously fitting the continuum and line emission. The effect of random errors are quantified by studying various fit-quality metrics, idealized recovery simulations and repeat observations. This analysis demonstrates that the emission lines are well-fit in the vast majority of the MaNGA dataset and the derived fluxes and errors are statistically robust. The systematic uncertainty on emission-line properties introduced by the choice of continuum templates is also discussed. In particular, we test the effect of using different stellar libraries and simple stellar-population models on the derived emission-line fluxes and the effect of introducing different tying prescriptions for the emission-line kinematics. We show that these effects can generate large (\(>\) 0.2 dex) discrepancies at low signal-to-noise and for lines with low equivalent width (EW); however, the combined effect is noticeable even for H\(\alpha\) EW \(>\) 6~\AA. We provide suggestions for optimal use of the data provided by SDSS data release 15 and propose refinements on the \DAP\ for future MaNGA data releases.
We present the first statistical investigation of spatially resolved emission-line properties in a sample of 63 low-mass galaxies at \(4\leq z<10\), using JWST/NIRSpec MSA data from the JWST Advanced ...Deep Extragalactic (JADES) survey focusing on deep, spatially resolved spectroscopy in the GOODS-S extragalactic field. By performing a stacking of the 2D spectra of the galaxies in our sample, we find an increasing or flat radial trend with increasing radius for OIII\(\lambda5007\)/H\(\beta\) and a decreasing one for NeIII\(\lambda3869\)/OII\(\lambda3727\) (3--4 \(\sigma\) significance). These results are still valid when stacking the sample in two redshift bins (i.e., \(4\leq z<5.5\) and \(5.5\leq z<10\)). The comparison with star-formation photoionization models suggests that the ionization parameter increases by \(\sim 0.5\) dex with redshift. We find a tentative metallicity gradient that increases with radius (i.e., 'inverted') in both redshift bins. Moreover, our analysis reveals strong negative gradients for the equivalent width of \Hbeta (7\(\sigma\) significance). This trend persists even after removing known AGN candidates, therefore, it is consistent with a radial gradient primarily in stellar age and secondarily in metallicity. Taken all together, our results suggest that the sample is dominated by active central star formation, with possibly inverted metallicity gradients sustained by recent episodes of accretion of pristine gas or strong radial flows. Deeper observations and larger samples are needed to confirm these preliminary results and to validate our interpretation.
H\(\alpha\) blobs are off-galaxy emission-line regions with weak or no optical counterparts. They are mostly visible in H\(\alpha\) line, appearing as concentrated blobs. Such unusual objects have ...been rarely observed and studied, and their physical origin is still unclear. We have identified 13 H\(\alpha\) blobs in the public data of MaNGA survey, by visually inspecting both the optical images and the spatially resolved maps of H\(\alpha\) line for \(\sim 4600\) galaxy systems. Among the 13 H\(\alpha\) blobs, 2 were reported in previously MaNGA-based studies and 11 are newly discovered. This sample, though still small in size, is by far the largest sample with both deep imaging and integral field spectroscopy. Therefore, for the first time we are able to perform statistical studies to investigate the physical origin of H\(\alpha\) blobs. We examine the physical properties of these H\(\alpha\) blobs and their associated galaxies, including their morphology, environments, gas-phase metallicity, kinematics of ionized gas, and ionizing sources. We find that the H\(\alpha\) blobs in our sample can be broadly divided into two groups. One is associated with interacting/merging galaxy systems, of which the ionization is dominated by shocks or diffuse ionized gas. It is likely that these H\(\alpha\) blobs used to be part of their nearby galaxies, but were stripped away at some point due to tidal interactions. The other group is found in gas-rich systems, appearing as low-metallicity star-forming regions that are visually detached from the main galaxy. These H\(\alpha\) blobs could be associated with faint disks, spiral arms, or dwarf galaxies.
