Abstract
We report results from a systematic wide-area search for faint dwarf galaxies at heliocentric distances from 0.3 to 2 Mpc using the full 6 yr of data from the Dark Energy Survey (DES). ...Unlike previous searches over the DES data, this search specifically targeted a field population of faint galaxies located beyond the Milky Way virial radius. We derive our detection efficiency for faint, resolved dwarf galaxies in the Local Volume with a set of synthetic galaxies and expect our search to be complete to
M
V
∼ (−7, −10) mag for galaxies at
D
= (0.3, 2.0) Mpc. We find no new field dwarfs in the DES footprint, but we report the discovery of one high-significance candidate dwarf galaxy at a distance of
2.2
−
0.12
+
0.05
Mpc
, a potential satellite of the Local Volume galaxy NGC 55, separated by 47′ (physical separation as small as 30 kpc). We estimate this dwarf galaxy to have an absolute
V
-band magnitude of
−
8.0
−
0.3
+
0.5
mag
and an azimuthally averaged physical half-light radius of
2.2
−
0.4
+
0.5
kpc
, making this one of the lowest surface brightness galaxies ever found with
μ
=
32.3
mag
arcsec
−
2
. This is the largest, most diffuse galaxy known at this luminosity, suggesting possible tidal interactions with its host.
Abstract
We report the detection of three RR Lyrae (RRL) stars (two RRc and one RRab) in the ultra-faint dwarf (UFD) galaxy Centaurus I (Cen I) and two Milky Way (MW)
δ
Scuti/SX Phoenicis stars based ...on multi-epoch
giz
DECam observations. The two RRc stars are located within two times the half-light radius (
r
h
) of Cen I, while the RRab star (CenI-V3) is at ∼6
r
h
. The presence of three distant RRL stars clustered this tightly in space represents a 4.7
σ
excess relative to the smooth distribution of RRL in the Galactic halo. Using the newly detected RRL stars, we obtain a distance modulus to Cen I of
μ
0
= 20.354 ± 0.002 mag (
σ
= 0.03 mag), a heliocentric distance of
D
⊙
= 117.7 ± 0.1 kpc (
σ
= 1.6 kpc), with systematic errors of 0.07 mag and 4 kpc. The location of the Cen I RRL stars in the Bailey diagram is in agreement with other UFD galaxies (mainly Oosterhoff II). Finally, we study the relative rate of RRc+RRd (RRcd) stars (
f
cd
) in UFD and classical dwarf galaxies. The full sample of MW dwarf galaxies gives a mean of
f
cd
= 0.28. While several UFD galaxies, such as Cen I, present higher RRcd ratios, if we combine the RRL populations of all UFD galaxies, the RRcd ratio is similar to the one obtained for the classical dwarfs (
f
cd
∼ 0.3). Therefore, there is no evidence for a different fraction of RRcd stars in UFD and classical dwarf galaxies.
Abstract
We present the second public data release (DR2) from the DECam Local Volume Exploration survey (DELVE). DELVE DR2 combines new DECam observations with archival DECam data from the Dark ...Energy Survey, the DECam Legacy Survey, and other DECam community programs. DELVE DR2 consists of ∼160,000 exposures that cover >21,000 deg
2
of the high-Galactic-latitude (∣
b
∣ > 10°) sky in four broadband optical/near-infrared filters (
g
,
r
,
i
,
z
). DELVE DR2 provides point-source and automatic aperture photometry for ∼2.5 billion astronomical sources with a median 5
σ
point-source depth of
g
= 24.3,
r
= 23.9,
i
= 23.5, and
z
= 22.8 mag. A region of ∼17,000 deg
2
has been imaged in all four filters, providing four-band photometric measurements for ∼618 million astronomical sources. DELVE DR2 covers more than 4 times the area of the previous DELVE data release and contains roughly 5 times as many astronomical objects. DELVE DR2 is publicly available via the NOIRLab Astro Data Lab science platform.
We report the discovery of six ultra-faint Milky Way satellites identified through matched-filter searches conducted using Dark Energy Camera (DECam) data processed as part of the second data release ...of the DECam Local Volume Exploration (DELVE) survey. Leveraging deep Gemini/GMOS-N imaging (for four candidates) as well as follow-up DECam imaging (for two candidates), we characterize the morphologies and stellar populations of these systems. We find that these candidates all share faint absolute magnitudes (MV ≥ -3.2 mag) and old, metal-poor stellar populations (τ > 10 Gyr, Fe/H < -1.4 dex). Three of these systems are more extended (r1/2 > 15 pc), while the other three are compact r1/2 < 10 pc). From these properties, we infer that the former three systems (Boötes V, Leo Minor I, and Virgo II) are consistent with ultra-faint dwarf galaxy classifications, whereas the latter three (DELVE 3, DELVE 4, and DELVE 5) are likely ultra-faint star clusters. Using data from the Gaia satellite, we confidently measure the proper motion of Boötes V, Leo Minor I, and DELVE 4, and tentatively detect a proper-motion signal from DELVE 3 and DELVE 5; no signal is detected for Virgo II. We use these measurements to explore possible associations between the newly discovered systems and the Sagittarius dwarf spheroidal, the Magellanic Clouds, and the Vast Polar Structure, finding several plausible associations. Our results offer a preview of the numerous ultra-faint stellar systems that will soon be discovered by the Vera C. Rubin Observatory and highlight the challenges of classifying the faintest stellar systems.
K-ras oncogene mutation has been shown to be a frequent event in pancreatic ductal adenocarcinomas induced by the carcinogen N-nitroso-bis(2-oxopropyl)amine in the hamster. The present study examines ...the mutational status of the K-ras oncogene in lesions that precede the appearance of invasive ductal adenocarcinomas. Syrian golden hamsters (80-100 g) received 12 weekly doses of 15 mg/kg N-nitroso-bis(2-oxopropyl)amine and were serially sacrificed at 8, 12, 14, 16, or 24 weeks following the initiation of treatment. Ten microns-thick sections of formalin-fixed paraffin-embedded pancreas were examined for hyperplasia, papillary hyperplasia, carcinoma in situ, and invasive and metastatic ductal carcinoma. Marked lesions of interest were scraped from the slide, subjected to polymerase chain reaction-mediated amplification of the first exon of the K-ras gene, and probed by oligonucleotide-specific hybridization for mutations at codon either 12 or 13. Of 186 samples assayed, K-ras codon 12 mutations were detected in 26% of hyperplasias, 46% of papillary hyperplasias, 76% of carcinoma in situ, 80% of adenocarcinomas, and 43% of lymph node metastases. Codon 12 mutations were exclusively G to A changes at the second position. Codon 13 mutations were only detected in 9 of 168 samples. These results suggest that K-ras activation is an early event in N-nitroso-bis(2-oxopropyl)amine-induced pancreatic carcinogenesis in the hamster.
High mol. wt genomic DNA was prepared from normal hamster pancreas and the solid and ascites variants of two different hamster transplantable carcinomas, one induced by N-nitrosobis(2-oxopropyl)amine ...and the other spontaneously occurring. This DNA was transfected into NIH/3T3 cells and resulted in cells that were capable of forming tumors when injected into nude mice. Analysis of the nude mouse tumors by Southern blotting revealed the presence of a band specific for hamster K-ras. Polymerase chain reaction (PCR)-mediated amplification of the K-ras codon 12-13 region of genomic DNA prepared from the transplantable tumors produced a 117 bp fragment which was analyzed by both allele-specific oligonucleotide hybridization and direct DNA sequencing. Oligonucleotide hybridization with probes specific for changes in the first or second position of codons 12 or 13 detected a G to A transversion in the second position of codon 12 in the chemically induced transplantable tumor, and a G to A change in the second position of codon 13 in the spontaneously occurring transplantable carcinomas. The result obtained for the chemically induced tumor was confirmed by direct dideoxy sequencing of the PCR-amplified product. These findings are the first to show a specific oncogene activation in an experimental pancreatic tumor model and also parallel the results recently reported for K-ras mutations in human pancreatic carcinoma.
We report the discovery and spectroscopic confirmation of an ultra-faint Milky Way (MW) satellite in the constellation of Leo. This system was discovered as a spatial overdensity of resolved stars ...observed with Dark Energy Camera (DECam) data from an early version of the third data release of the DECam Local Volume Exploration survey (DELVE EDR3). The low luminosity (\(M_V = -3.56_{-0.37}^{+0.47}\); \(L_V = 2300_{-800}^{+1000} L_\odot\)), large size (\(r_{1/2} = 90_{-30}^{+30}\) pc), and large heliocentric distance (\(D = 111_{-4}^{+7}\) kpc) are all consistent with the population of ultra-faint dwarf galaxies (UFDs). Using Keck/DEIMOS observations of the system, we were able to spectroscopically confirm 11 member stars, while measuring a mass to light ratio of \(1000_{-700}^{+1900} M_\odot/L_\odot\) and a non-zero metallicity dispersion of \(\sigma_{\rm Fe/H}=0.33_{-0.14}^{+0.19}\), further confirming Leo VI's identity as an UFD. While the system has an highly elliptical shape, \(\epsilon = 0.54_{-0.29}^{+0.19}\), we do not find any evidence that it is tidally disrupting. Moreover, despite its apparent on-sky proximity to members of the proposed Crater-Leo infall group, its relatively lower heliocentric distance and inconsistent position in energy-angular momentum space with the other group members make it unlikely for it to be part of the proposed infall group.
We present a spectroscopic analysis of Eridanus IV (Eri IV) and Centaurus I (Cen I), two ultra-faint dwarf galaxies of the Milky Way. Using IMACS/Magellan spectroscopy, we identify 28 member stars of ...Eri IV and 34 member stars of Cen I. For Eri IV, we measure a systemic velocity of \(v_{sys} = -31.5^{+1.3}_{-1.2}\:\mathrm{km\:s^{-1}}\) and velocity dispersion \(\sigma_{v}= 6.1^{+1.2}_{-0.9}\:\mathrm{km\:s^{-1}}\). Additionally, we measure the metallicities of 16 member stars of Eri IV. We find a metallicity of \(\mathrm{Fe/H}=-2.87^{+0.08}_{-0.07}\) and resolve a dispersion of \(\sigma_{\mathrm{Fe/H}} = 0.20\pm0.09\). The mean metallicity is marginally lower than all other known ultra-faint dwarf galaxies, making it one of the most metal-poor galaxies discovered thus far. Eri IV also has a somewhat unusual right-skewed metallicity distribution. For Cen I, we find a velocity \(v_{sys} = 44.9\pm0.8\:\mathrm{km\:s^{-1}}\) and velocity dispersion \(\sigma_{v} = 4.2^{+0.6}_{-0.5} \:\mathrm{km\:s^{-1}}\). We measure the metallicities of 27 member stars of Cen I, and find a mean metallicity \(\mathrm{Fe/H} = -2.57\pm0.08\) and metallicity dispersion \(\sigma_{\mathrm{Fe/H}} = 0.38^{+0.07}_{-0.05}\). We calculate the systemic proper motion, orbit, and the astrophysical J-factor for each system, the latter of which indicates that Eri IV is a good target for indirect dark matter detection. We also find no strong evidence for tidal stripping of Cen I or Eri IV. Overall, our measurements confirm that Eri IV and Cen I are dark matter-dominated galaxies with properties largely consistent with other known ultra-faint dwarf galaxies. The low metallicity, right-skewed metallicity distribution, and high J-factor make Eri IV an especially interesting candidate for further followup.
Cellular retinoic acid-binding protein (CRABP) was detected in the nuclear fraction of N-methyl-N-nitrosourea-induced mammary cancers after the incubation of cytosol containing 3Hretinoic acid ...(RA)-bound CRABP with isolated nuclei. CRABP extracted from the nuclei in buffer containing 0.4 M-KCl sedimented as a 2 S component when subjected to sucrose-density-gradient analysis. 3HRA-CRABP was found to be a prerequisite for the detection of nuclear binding, since the incubation of isolated nuclei or 0.4 M-KCl extract of the nuclei with 3HRA did not result in any significant binding. Incubation of 3HRA-CRABP at 25 or 30 degrees C before incubation with the nuclei neither altered the sedimentation coefficient nor enhanced the nuclear binding compared with 0 degrees C incubation. The tumour nuclei contained a saturable number of binding sites with a dissociation constant of 1.6 x 10(-9) M. These results indicate that the action of retinoic acid in the target organ may be mediated by its interaction with the nuclei.
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