We present results derived from the first multi-chord stellar occultations by the transneptunian object (50000) Quaoar, observed on 2011 May 4 and 2012 February 17, and from a single-chord occultation observed on 2012 October 15. If the timing of the five chords obtained in 2011 were correct, then Quaoar would possess topographic features (crater or mountain) that would be too large for a body of this mass. An alternative model consists in applying time shifts to some chords to account for possible timing errors. Satisfactory elliptical fits to the chords are then possible, yielding an equivalent radius R equiv = 555±2.5 km and geometric visual albedo p V = 0.109±0.007. Assuming that Quaoar is a Maclaurin spheroid with an indeterminate polar aspect angle, we derive a true oblateness of = 0.087 +0.0268 −0.0175 , an equatorial radius of 569 +24 −17 km, and a density of 1.99 ± 0.46 g cm −3 . The orientation of our preferred solution in the plane of the sky implies that Quaoar's satellite Weywot cannot have an equatorial orbit. Finally, we detect no global atmosphere around Quaoar, considering a pressure upper limit of about 20 nbar for a pure methane atmosphere.

In the years to come, the Javalambre-Physics of the Accelerated Universe Astrophysical Survey (J-PAS) will observe 8000 deg2 of the northern sky with 56 photometric bands. J-PAS is ideal for the detection of nebular emission objects. This paper presents a new method based on artificial neural networks (ANNs) that is aimed at measuring and detecting emission lines in galaxies up to z = 0.35. These lines are essential diagnostics for understanding the evolution of galaxies through cosmic time. We trained and tested ANNs with synthetic J-PAS photometry from CALIFA, MaNGA, and SDSS spectra. To this aim, we carried out two tasks. First, we clustered galaxies in two groups according to the values of the equivalent width (EW) of Hα, Hβ, [N II], and [O III] lines measured in the spectra. Then we trained an ANN to assign a group to each galaxy. We were able to classify them with the uncertainties typical of the photometric redshift measurable in J-PAS. Second, we utilized another ANN to determine the values of those EWs. Subsequently, we obtained the [N II]/Hα, [O III]/Hβ, and O 3N 2 ratios, recovering the BPT diagram ([O III]/Hβ versus [N II]/Hα). We studied the performance of the ANN in two training samples: one is only composed of synthetic J-PAS photo-spectra (J-spectra) from MaNGA and CALIFA (CALMa set) and the other one is composed of SDSS galaxies. We were able to fully reproduce the main sequence of star-forming galaxies from the determination of the EWs. With the CALMa training set, we reached a precision of 0.092 and 0.078 dex for the [N II]/Hα and [O III]/Hβ ratios in the SDSS testing sample. Nevertheless, we find an underestimation of those ratios at high values in galaxies hosting an active galactic nuclei. We also show the importance of the dataset used for both training and testing the model. Such ANNs are extremely useful for overcoming the limitations previously expected concerning the detection and measurements of the emission lines in such surveys as J-PAS. Furthermore, we show the capability of the method to measure a EW of 10 Å in Hα, Hβ, [N II] and [O III] lines with a signal-to-noise ratio (S/N) of 5, 1.5, 3.5, and 10, respectively, in the photometry. Finally, we compare the properties of emission lines in galaxies observed with miniJPAS and SDSS. Despite the limitation of such a comparison, we find a remarkable correlation in their EWs.

Stellar population studies of early-type galaxies (ETGs) based on their optical stellar continuum suggest that these are quiescent systems. However, emission lines and ultraviolet photometry reveal a diverse population. We use a new version of the starlight spectral synthesis code and state-of-the-art stellar population models to simultaneously fit SDSS spectra and GALEX photometry for a sample of 3453 galaxies at z < 0.1 with NUV − r > 5 that are classified as elliptical by Galaxy Zoo. We reproduce FUV magnitudes for 80 per cent of UV upturn galaxies selected using criteria from the literature, suggesting that additional stellar population ingredients such as binaries and extreme horizontal branch stars may have a limited contribution to the UV upturn. The addition of ultraviolet data leads to a broadening of the distributions of mean stellar ages, metallicities and attenuation. Stellar populations younger than 1 Gyr are required to reproduce the ultraviolet emission in 17 per cent of our sample. These systems represent 43 per cent of the sample at 5 < NUV − r < 5.5 and span the same stellar mass range as other ETGs in our sample. ETGs with young stellar components have larger Hα equivalent widths (WHα) and larger dust attenuation. Emission line ratios and WHα indicate that the ionising source in these systems is a mixture of young and old stellar populations. Their young stellar populations are metal-poor, especially for high-mass galaxies, indicating recent star formation associated with rejuvenation events triggered by external processes, such as minor mergers.

The Javalambre-Physics of the Accelerating Universe Astrophysical Survey (J-PAS) is expected to map thousands of square degrees of the northern sky with 56 narrowband filters (spectral resolution of R ∼ 60) in the upcoming years. This resolution allows us to study emission line galaxies (ELGs) with a minimum equivalent width of 10 Å in the Hα emission line for a median signal-to-noise ratio (S/N) of 5. This will make J-PAS a very competitive and unbiased emission line survey compared to spectroscopic or narrowband surveys with fewer filters. The miniJPAS survey covered 1 deg2, and it used the same photometric system as J-PAS, but the observations were carried out with the pathfinder J-PAS camera. In this work, we identify and characterize the sample of ELGs from miniJPAS with a redshift lower than 0.35, which is the limit to which the Hα line can be observed with the J-PAS filter system. Using a method based on artificial neural networks, we detect the ELG population and measure the equivalent width and flux of the Hα, Hβ, [O III], and [N II] emission lines. We explore the ionization mechanism using the diagrams [OIII]/Hβ versus [NII]/Hα (BPT) and EW(Hα) versus [NII]/Hα (WHAN). We identify 1787 ELGs (83%) from the parent sample (2154 galaxies) in the AEGIS field. For the galaxies with reliable EW values that can be placed in the WHAN diagram (2000 galaxies in total), we obtained that 72.8 ± 0.4%, 17.7 ± 0.4%, and 9.4 ± 0.2% are star-forming (SF), active galactic nucleus (Seyfert), and quiescent galaxies, respectively. The distribution of EW(Hα) is well correlated with the bimodal color distribution of galaxies. Based on the rest-frame (u − r)–stellar mass diagram, 94% of the blue galaxies are SF galaxies, and 97% of the red galaxies are LINERs or passive galaxies. The nebular extinction and star formation rate (SFR) were computed from the Hα and Hβ fluxes. We find that the star formation main sequence is described as log SFR [M⊙ yr−1] = 0.90−0.02+0.02 log M⋆[M⊙]−8.85−0.20+0.19 and has an intrinsic scatter of 0.20−0.01+0.01. The cosmic evolution of the SFR density (ρSFR) is derived at three redshift bins: 0 <  z ≤ 0.15, 0.15 <  z ≤ 0.25, and 0.25 <  z ≤ 0.35, which agrees with previous results that were based on measurements of the Hα emission line. However, we find an offset with respect to other estimates that were based on the star formation history obtained from fitting the spectral energy distribution of the stellar continuum. We discuss the origin of this discrepancy, which is probably a combination of several factors: the escape of ionizing photons, the SFR tracers, and dust attenuation, among others.

MUSE-based emission-line maps of the spiral galaxy NGC 4030 reveal the existence of unresolved sources with forbidden line emission enhanced with respect to those seen in its own H ii regions. This study reports our efforts to detect and isolate these objects and identify their nature. Candidates are first detected as unresolved sources on an image of the second principal component of the H β, [O iii] 5007, H α, [N ii] 6584, [S ii] 6716, 6731 emission-line data cube, where they stand out clearly against both the dominant H ii region population and the widespread diffuse emission. The intrinsic emission is then extracted accounting for the highly inhomogeneous emission-line ‘background’ throughout the field of view. Collisional to recombination line ratios like [S ii]/H α, [N ii]/H α, and [O i]/H α tend to increase when the background emission is corrected for. We find that many (but not all) sources detected with the principal component analysis have properties compatible with supernova remnants (SNRs). Applying a combined [S ii]/H α and [N ii]/H α classification criterion leads to a list of 59 sources with SNR-like emission lines. Many of them exhibit conspicuous spectral signatures of SNRs around 7300 Å, and a stacking analysis shows that these features are also present, except weaker, in other cases. At nearly 30 Mpc, these are the most distant SNRs detected by optical means to date. We further report the serendipitous discovery of a luminous (MV ∼ −12.5), blue, and variable source, possibly associated with a supernova impostor.