The nearby universe remains the best laboratory to understand physical properties of galaxies and is a reference for any comparison with high redshift observations. The all sky (or very large) surveys performed from the ultraviolet (UV) to the far-infrared (far-IR) gives us large datasets with a very large wavelength coverage to perform a reference study. We want to investigate dust attenuation characteristics as well as star formation rate (SFR) calibrations on a sample of nearby galaxies observed over 13 bands from 0.15 to 160 microns. A sample of 363 galaxies is built from the AKARI /FIS all sky survey cross-correlated with SDSS and GALEX surveys. Broad band spectral energy distributions are fitted with the CIGALE code optimized to analyze variations in dust attenuation curves and SFR measurements and based on an energetic budget between the stellar and dust emission. Our galaxy sample is primarily selected in far-IR and mostly constituted of massive, actively star forming galaxies. There is some evidence for a dust attenuation law slightly steeper than that used for starburst galaxies but we are unable to constrain the presence or not of a bump at 220 nm. We confirm that a time dependent dust attenuation is necessary to perform the best fits. Various calibrations of the dust attenuation in the UV as a function of UV-optical colours are discussed. A calibration of the current star formation rate combining UV and total IR emissions is proposed with an accurate estimation of dust heating by old stars: for the whole sample 17 % of the total dust luminosity is not related to the recent star formation
Star formation and dust extinction properties of local galaxies from AKARI-GALEX All-Sky Surveys: First results from most secure multiband sample from FUV to FIR
GALEX far-UV color selection of UV-bright high-redshift quasars
我们研究了GALEX探测到的z>2.7类星体的小种群,它们的远紫外辐射不会被HI莱曼极限系统所熄灭。这些类星体对于探测沿其视线的星系间HeII吸收具有特别重要的意义。我们将已验证的z>2.7类星体与GALEX GR 4源目录相关联,得到304个S/N>3的源。然而,其中约50%仅在GALEX NUV波段检测到,这表明低红移莱曼极限系统截断了FUV通量。我们利用GALEX UV颜色挑选最有希望的目标进行后续研究,蓝色(红色)GALEX颜色表示透明(不透明)视线。蒙特卡罗模拟表明,在z<3.5时,FUV-NUV<1的类星体的HeII探测率约为60%,比不包括颜色信息的GALEX搜索增加了约50%。我们认为在S/N>3时探测到的52个类星体是最有希望进行HST后续观测的,如果我们考虑在FUV中探测到S/N>2,则还有114个类星体。SDSS只提供了SDSS和GALEX应该探测到的NUV亮类星体的一半。我们修正了SDSS类星体选择函数,发现SDSS系统地错过了在3<z<3.5处具有蓝色u-g<2颜色的类星体,这是由于与颜色空间中的恒星轨迹重叠。我们的颜色相关的SDSS选择函数自然地解释了具有红移的SDSS类星体的不均匀u-g颜色分布以及颜色选择和射电选择的SDSS类星体之间的颜色差异。此外,它产生了很好的协议之间的观测和预测的紫外亮SDSS类星体的数量。我们证实了我们以前的主张,SDSS优…
Ten More New Sightlines for the Study of Intergalactic Helium, and Hundreds of Far-UV-Bright Quasars, from SDSS, GALEX, and HST
沿类星体视线的吸收仍然是在大部分星系际介质(IGM)中HeII再电离的最敏感的直接措施之一。直到最近,只有不到六个适合于HeII Gunn-Peterson测试的未被遮蔽的类星体视线被发现;虽然这些少数人表现出很大的希望,但小样本量限制了宇宙学推断的信心。我们最近又增加了9个这样的干净的HeII类星体,利用SDSS类星体样本,GALEX的宽带紫外成像和HST的高产紫外光谱确认。在这里,我们通过将SDSS DR 7和GALEX GR 4 +5交叉关联到目录428个SDSS和165个z>2.78的其他类星体来显着扩展这种方法,这些类星体可能(~70%)有GALEX检测,这表明它们在远紫外线下是明亮的。侦察HST周期16补充棱镜数据为29个这些新的类星体GALEX匹配光谱确认17确实远紫外明亮。这些确认中至少有10个具有清晰的视线,一直到HeII莱曼α,大大增加了已知的干净HeII类星体的数量,并重申了我们的选择技术的数量级提高了效率。将这个项目和我们过去的项目的确认结合起来,产生了二十多个HeII类星体,使样本增加了五倍。这些提供了实质性的进展,朝向样本的HeII类星体的视线足够大,并跨越足够的红移范围,使统计IGM研究,可能会避免个别对象的特殊性和视线的变化。我们扩展的数百个高可能性远紫外亮类星体的目录也将有助于理解类星体本身的极端紫外特性。
We present the 9 and 18 micron luminosity functions (LFs) of galaxies at 0.006 < z < 0.8 (with an average redshift of ~ 0.04) using the AKARI mid-infrared all-sky survey catalog. We selected 243 galaxies at 9 micron and 255 galaxies at 18 micron from the Sloan Digital Sky Survey (SDSS) spectroscopy region. These galaxies were then classified by their optical emission lines, such as the line width of H_alpha or by their emission line ratios of [OIII]/H_beta and [NII]/H_alpha into five types: Type 1 active galactic nuclei (AGN) (Type 1); Type 2 AGN (Type 2); low-ionization narrow emission line g…
The north ecliptic pole (NEP) field is a natural deep field location for many satellite observations. It has been targeted manytimes since it was surveyed by the AKARI space telescope with its unique wavelength coverage from the near- to mid-infrared(mid-IR). Many follow-up observations have been carried out and made this field one of the most frequently observed areas witha variety of facilities, accumulating abundant panchromatic data from X-ray to radio wavelength range. Recently, a deep opticalsurvey with the Hyper Suprime-Cam (HSC) at the Subaru telescope covered the NEP-Wide (NEPW) field…
We explore the distribution of cool (~$10^4$K) gas around galaxies and its dependence on galaxy properties. By cross-correlating about 50,000 MgII absorbers with millions of sources from the SDSS (optical), WISE (IR), and GALEX (UV) surveys we effectively extract about 2,000 galaxy-absorber pairs at z~0.5 and probe relations between absorption strength and galaxy type, impact parameter and azimuthal angle. We find that cool gas traced by MgII absorbers exists around both star-forming and passive galaxies with a similar incidence rate on scales greater than 100 kpc but each galaxy type exhibits…
The Slow Death (or Rebirth?) of Extended Star Formation in z~0.1 Green Valley Early-Type Galaxies
在本地宇宙中的紫外线观测发现了一个人口的早期型星系的紫外线通量符合低水平的最近或正在进行的恒星形成。我们提出了19个SDSS早型星系样本的解析紫外光光度测量,这些星系来自Salim & Rich(2010)最初选择的样本,位于GALEX测量的紫外光色星等图中绿谷的蓝色部分。利用高分辨率的HST远紫外成像提供了独特的洞察这些星系中的紫外光分布,我们称之为“扩展的恒星形成早期型星系”(ESF-ETG),因为扩展的紫外辐射表明最近的恒星形成。所有ESF-ETG的UV-光学颜色曲线显示红色中心和蓝色外部部分。它们的外部颜色需要在紫外线明亮区域存在大量的老年恒星。叠加的SDSS光谱分析表明,在他们的中心弱LINER样发射。使用交叉匹配的SDSS DR 7/GALEX GR 6目录,我们搜索了与这些ESF-ETG具有相似性质的其他绿谷星系,并估计约13%的具有相似恒星质量和紫外光学颜色的尘埃校正的绿谷星系可能是ESF候选者,即,ESF-ETG并不罕见。我们的研究结果与现有盘中逐渐下降的恒星形成一致,即,ESF-ETG第一次演化到红色序列,或者由于旧盘中的吸积气体而再生的恒星形成,前提是气体不会破坏星系的结构,并且由此产生的恒星形成不是太近和突发的。ESF-ETG可能代表了一个重要的星系亚群,它们可以在绿谷中逗留长达几个Gyrs,这是基于它们与附近富含气体的绿谷星系的相似之处,这些星系具有低水平…
We explore the co-evolution of galaxies in nearby groups (V < 3000 km/s) with a multi-wavelength approach. We analyze GALEX far-UV (FUV) and near-UV (NUV) imaging and SDSS u,g,r,i,z data of groups spanning a large range of dynamical phases. We characterize the photometric properties of spectroscopically-confirmed galaxy members and investigate the global properties of the groups through a dynamical analysis. Here we focus on NGC 5846, the third most massive association of Early-Type Galaxies (ETG) after the Virgo and Fornax clusters. The group, composed of 90 members, is dominated by ETGs (abo…
The properties of Brightest Cluster Galaxies in the SDSS DR6 adaptive matched filter cluster catalogue
我们研究了基于自适应匹配滤波器技术(AMF,Szabo等人,2010年)。我们的样本包括超过14300个星系的红移范围为0.1-0.3。我们测试的目录显示,它包括著名的BCGs在于SDSS足迹。我们的特征BCGs的r-波段光度和光学颜色,以及它们的红移趋势。特别是,我们定义和研究的蓝色BCGs的分数,即那些可能会错过基于颜色的聚类调查和目录。较富裕的集群往往有更明亮的BCG,但不那么占主导地位,比穷人的系统。我们的BCG中有4-9%的BCG在g-r色上至少比红序列在它们给定的红移上蓝0.3等。对于丰度高于50的簇,这样的分数降低到1-6%,其中3%的BCGs低于红色序列0.5等。初步的形态学研究表明,在较低的丰度蓝色部分的增加可能有一个不可忽视的贡献,从螺旋星系。我们表明,基于g-r红色序列或基于颜色u-r >2.2的切割的颜色选择可能导致错过大多数这样的蓝色BCGs。我们还将颜色分析扩展到紫外线范围,将我们的产品目录与Galex GR 4和GR 5的公开数据进行交叉匹配。我们显示了一个明确的相关性从光学红色序列的偏移量和紫外线过量。最后,我们将我们的目录与ACCEPT聚类样本(Cavagnolo等人,2009),并发现蓝色BCGs倾向于在低熵和短冷却时间的集群中。也就是说,蓝光可能是由于最近的恒星形成与冷却流提供的气体有关。(节略)
We present the mean spectral energy distribution (SED) of a sample of optically selected quasars (QSOs) at redshifts of $1 \le z \le 5$. To derive it, we exploit photometric information from SDSS, UKIDSS, and WISE surveys in combination with a stacking analysis of \textit{Herschel}, \textit{AKARI}, and \textit{Planck} maps at the location of the QSOs. The near-UV and optical parts of the reconstructed mean rest-frame SED are similar to those found in other studies. However, the SED shows an excess at 1-2 $μ$m (when compared to the aforementioned SEDs normalized in the near-UV) and a prominent …
We present the final Sloan Digital Sky Survey IV (SDSS-IV) quasar catalog from Data Release 16 of the extended Baryon Oscillation Spectroscopic Survey (eBOSS). This catalog comprises the largest selection of spectroscopically confirmed quasars to date. The full catalog includes two sub-catalogs: a "superset" of all SDSS-IV/eBOSS objects targeted as quasars containing 1,440,615 observations and a quasar-only catalog containing 750,414 quasars, including 225,082 new quasars appearing in an SDSS data release for the first time, as well as known quasars from SDSS-I/II/III. We present automated ide…