Magnetic imprints, the rapid and irreversible evolution of photospheric magnetic fields as feedback from flares in the corona, have been confirmed by many previous studies. These studies showed that ...the horizontal field will permanently increase at the polarity inversion line (PIL) after eruptions, indicating that a more horizontal geometry of the photospheric magnetic field is produced. In this study, we analyze 20 X-class flares since the launch of the Solar Dynamics Observatory in 15 active regions with heliographic angles no greater than 45°. We observe clear magnetic imprints in 16 flares, whereas 4 flares are exceptional. The imprint regions of the horizontal field are located not only at the PIL but also at sunspot penumbra with strong vertical fields. Making use of the observed mass and speed of the corresponding coronal mass ejections (CMEs), we find that the CMEs with larger momenta are associated with stronger magnetic imprints. Furthermore, a linear relationship, with a Kendall's Tau-b coefficient 0.54, between the CME momentum and the change of Lorentz force, is revealed. Based on that, we quantify the back reaction time to be ∼70 s, with a 90% confidence interval from about 50 to 90 s.
Abstract
The role of active galactic nuclei (AGNs) during galaxy interactions and how they influence the star formation in the system are still under debate. We use a sample of 1156 galaxies in ...galaxy pairs or mergers (hereafter “pairs”) from the MaNGA survey. This pair sample is selected by the velocity offset, projected separation, and morphology, and is further classified into four cases along the merger sequence based on morphological signatures. We then identify a total of 61 (5.5%) AGNs in pairs based on the emission-line diagnostics. No evolution of the AGN fraction is found, either along the merger sequence or compared to isolated galaxies (5.0%). We observe a higher fraction of passive galaxies in galaxy pairs, especially in the pre-merging cases, and associate the higher fraction to their environmental dependence. The isolated AGN and AGNs in pairs show similar distributions in their global stellar mass, star-formation rate (SFR), and central O
iii
surface brightness. AGNs in pairs show radial profiles of increasing specific SFR and declining Dn4000 from center to outskirts, and no significant difference from the isolated AGNs. This is clearly different from star-forming galaxies (SFGs) in our pair sample, which show enhanced central star formation, as reported before. AGNs in pairs have lower Balmer decrements at outer regions, possibly indicating less dust attenuation. Our findings suggest that AGNs are likely follow an inside-out quenching and the merger impact on the star formation in AGNs is less prominent than in SFGs.
Abstract
We identify a sample of spectroscopically measured emission line galaxy (ELG) Pairs up to
z
= 1.6 from the Wide Field Camera 3 (WFC3) Infrared Spectroscopic Parallels (WISP) survey. WISP ...obtained slitless, near-infrared grism spectroscopy along with direct imaging in the
J
and
H
bands by observing in the pure-parallel mode with the WFC3 on board the Hubble Space Telescope. From our search of 419 WISP fields covering an area of ∼0.5 deg
2
, we find 413 ELG pair systems, mostly H
α
emitters. We then derive reliable star formation rates (SFRs) based on the attenuation-corrected H
α
fluxes. Compared to isolated galaxies, we find an average SFR enhancement of 40%–65%, which is stronger for major Pairs and Pairs with smaller velocity separations (Δ
v
< 300 km s
−1
). Based on the stacked spectra from various subsamples, we study the trends of emission line ratios in pairs, and find a general consistency with enhanced lower ionization lines. We study the pair fraction among ELGs, and find a marginally significant increase with redshift
f
∝ (1 +
z
)
α
, where the power-law index
α
= 0.58 ± 0.17 from
z
∼ 0.2 to ∼1.6. The fraction of active galactic nuclei is found to be the same in the ELG Pairs as compared to the isolated ELGs.
Abstract
We present redshifts for 2753 low-redshift galaxies between 0.03 ≲
z
spec
≲ 0.5 with 18 ≤
r
≤ 22 obtained with Hectospec at the Multi-Mirror Telescope. The observations targeted the XMM-LSS, ...ELAIS-N1 and DEEP2-3 fields, each of which covers ∼1 deg
2
. These fields are also part of the recently completed Canada–France–Hawaii Telescope Large Area
U
-band Deep Survey and ongoing Hyper Suprime-Cam deep fields surveys. The efficiency of our technique for selecting low-redshift galaxies is confirmed by the redshift distribution of our sources. In addition to redshifts, these high signal-to-noise ratio spectra are used to measure ages, metallicities, and nuclear activity levels. In combination with the photometric catalog in
u
,
g
,
r
,
i
,
z
,
y
down to 27 AB mag, we are able to study the galaxy population down to stellar masses of ∼10
8
M
⊙
. This paper presents the observational strategy, the reduction procedure and properties of the galaxy sample. (The catalog can be accessed through the survey’s website at
http://mips.as.arizona.edu/~cnaw/Faint_Low_z/
.)
Magnetic imprints, the rapid and irreversible evolution of photospheric magnetic fields as a feedback from flares in the corona, have been confirmed by many previous studies. These studies showed ...that the horizontal field will permanently increase at the polarity inversion line (PIL) after eruptions, indicating that a more horizontal geometry of photospheric magnetic field is produced. In this study, we analyze 20 X-class flares since the launch of the Solar Dynamics Observatory (SDO) in 15 active regions (ARs) with heliographic angle no greater than 45 degrees. We observe clear magnetic imprints in 16 flares, whereas 4 flares are exceptional. The imprint regions of the horizontal field are located not only at the PIL but also at sunspot penumbra with strong vertical fields. Making use of the observed mass and speed of the corresponding coronal mass ejections (CMEs) , we find that the CMEs with larger momenta are associated with stronger magnetic imprints. Furthermore, a linear relationship, with a Kendall's Tau-b coefficient 0.54, between the CME momentum and the change of Lorentz force is revealed. Based on that, we quantify the back reaction time to be around 70 s, with a 90% confidence interval from about 50 s to 90 s.
The Spitzer Extended Deep Survey (SEDS) as a deep and wide mid-infrared (MIR) survey project provides a sample of 500000+ sources spreading 1.46 square degree and a depth of 26 AB mag (3\(\sigma\)). ...Combining with the previous available data, we build a PSF-matched multi-wavelength photometry catalog from u band to 8\(\mu\)m. We fit the SEDS galaxies spectral energy distributions by the local galaxy templates. The results show that the SEDS galaxy can be fitted well, indicating the high redshift galaxy (\(z \sim 1\)) shares the same templates with the local galaxies. This study would facilitate the further study of the galaxy luminosity and high redshift mass function.
The role of active galactic nuclei (AGNs) during galaxy interactions and how they influence the star formation in the system are still under debate. We use a sample of 1156 galaxies in galaxy pairs ...or mergers (hereafter `pairs') from the MaNGA survey. This pair sample is selected by the velocity offset, projected separation, and morphology, and is further classified into four cases along the merger sequence based on morphological signatures. We then identify a total of 61 (5.5%) AGNs in pairs based on the emission-line diagnostics. No evolution of the AGN fraction is found, either along the merger sequence or compared to isolated galaxies (5.0%). We observe a higher fraction of passive galaxies in galaxy pairs, especially in the pre-merging cases, and associate the higher fraction to their environmental dependence. The isolated AGN and AGN in pairs show similar distributions in their global stellar mass, star formation rate (SFR), and central OIII surface brightness. AGNs in pairs show radial profiles of increasing specific SFR and declining Dn4000 from center to outskirts, and no significant difference from the isolated AGNs. This is clearly different from star-forming galaxies (SFGs) in our pair sample, which show enhanced central star formation, as reported before. AGNs in pairs have lower Balmer decrements at outer regions, possibly indicating less dust attenuation. Our findings suggest that AGNs likely follow an inside-out quenching and the merger impact on the star formation in AGNs is less prominent than in SFGs.
We identify a sample of spectroscopically measured emission line galaxy (ELG) pairs up to z=1.6 from the WFC3 Infrared Spectroscopic Parallels (WISP) survey. WISP obtained slitless, near-infrared ...grism spectroscopy along with direct imaging in the J and H bands by observing in the pure-parallel mode with the Wide Field Camera Three (WFC3) on the Hubble Space Telescope (HST). From our search of 419 WISP fields covering an area of ~0.5 deg\(^{2}\), we find 413 ELG pair systems, mostly Halpha emitters. We then derive reliable star formation rates (SFRs) based on the attenuation-corrected Halpha fluxes. Compared to isolated galaxies, we find an average SFR enhancement of 40%-65%, which is stronger for major pairs and pairs with smaller velocity separations (Delta_v < 300 km/s). Based on the stacked spectra from various subsamples, we study the trends of emission line ratios in pairs, and find a general consistency with enhanced lower-ionization lines. We study the pair fraction among ELGs, and find a marginally significant increase with redshift \(f \propto (1+z)^\alpha\), where the power-law index \alpha=0.58\(\pm\)0.17 from \(z\sim\)0.2 to \(z\sim\)1.6. The fraction of Active galactic Nuclei (AGNs), is found to be the same in the ELG pairs as compared to isolated ELGs.
We present redshifts for 2753 low-redshift galaxies between \(0.03 \lesssim z_{\rm spec}\lesssim0.5\) with 18 \(\leq\) \(r\) \(\leq\) 22 obtained with Hectospec at the Multi-Mirror Telescope (MMT). ...The observations targeted the XMM-LSS, ELAIS-N1 and DEEP2-3 fields, each of which covers \(\sim\) 1 deg\(^2\). These fields are also part of the recently completed CFHT Large Area U-band Deep Survey (CLAUDS) and on-going Hyper Suprime-Cam deep fields surveys. The efficiency of our technique for selecting low-redshift galaxies is confirmed by the redshift distribution of our sources. In addition to redshifts, these high S/N spectra are used to measure ages, metallicities, and nuclear activity levels. In combination with the photometric catalogue in \(u\), \(g\), \(r\), \(i\), \(z\), \(y\) down to 27 AB mag, we are able to study the galaxy population down to stellar masses of \(\sim\) 10\(^8 M_\odot\) . This paper presents the observational strategy, the reduction procedure and properties of the galaxy sample.
PDF
