# Presentation: 755851

## The 8 O'clock Arc

- Sahar Allam
- U  Wyoming/Fermilab
- Searching for Strong Lenses in Large Imaging
- Fermilab
- June 14-15, 2007
- The era before the SDSS
- SDSS contribution
- Current and future follow-up plan

**Notes:**
On behalf of the organizing committee I would like to thank you all for coming.
My name is Allam, and 

Strongly lensed galaxies are particularly useful for studies of galaxy evolution due to the 
magnification of the galaxy flux: since surface brightness is conserved by lensing, the 
stretching of the galaxy shape increases the apparent brightness of the source galaxy. 
These apparently brighter objects are then prime candidates for detailed follow-up studies 
at a fraction of the telescope time that would be necessary for comparable but unlensed galaxies. 

##  1890s

- Q0957+561
- The first GL
- 1979

- MG1131+0456
- The first
- Einstein ring,
- 1988

- QSO 2237+0305
- The first
- Einstein cross
- 1985

-  1890s
-  Einstein 1912, 1936
-  Fritz Zwicky 1937 (why not galaxies)
-    “gravitational telescopes”
-  1960s first QSO was discovered

**Notes:**
The  idea  that a massive object could act as retractor to bend the light of  a source behind was first  
introduced  in  1890s later on G.L.  were used  to prove the  Einstein  general
relativity theory (Einstein 1912, 1936). A year later Fritz Zwicky 1937 suggested that a galaxy can 
Act as gravitational telescopes. After the discovery of QSOs in 1960s, 1979, the first lensed 
Q0957+561 was discovered
In 1985, The first Einstein cross was discovered
And in 1988 MG1131+0456, The first Einstein ring was discovered
Now it is well establish that G.L. offer a: 
-Unique window to probe  the lensed galaxy, it mass and its dark matter content
-Unique window to study high redshifted object that would not be possible 
without the extra power of the gravitational telescope

## The need for the SDSS 

- ~1000(s) of high redshift objects may be gravitationally lensed, so we need to examine very large areas of sky.
- Identification of a strong lens system hinges on achromatic nature of lensing, so multi-colour imaging is of enormous value.
- + 10e6 spectra

**Notes:**

If there are at least 1000s of high redshift object that are gravitationally lensed, so to find them we 
need multi color imaging survey of a large area of the sky. Which make the SDSS data set available 
recourse. 
Indeed he SDSS provide a unique opportunity to search for QL.
The SDSS  use it’s dedicated 2.5m telescope at APO, with 3 degree field of view. 
It is actually 2 surveys in one
1- Imaging one quarter of the sky in 5 SDSS bands, 
and then select candidate for spectroscopy follow up using 640 fiber spectrographs. 
SDSS completed its first phase of operations — SDSS-I — in June, 2005.
 Over the course of five years, SDSS-I imaged more than 8,000 square degrees of the sky in 
five bandpasses, detecting nearly 200 million celestial objects, and it measured spectra of more 
than 675,000 galaxies, 90,000 quasars, and 185,000 stars. 
For more about the SDSSI, and SDSSII  please see the SDSS web page.
The need for the SDSS one quorter of the sky is imaged in five color bands which +
10^6 galaxy spectra, + 10^5 of QSO spectra, the SDSS sample

## SDSS

**2.5m telescope, APO, NM**
***	******3 degree field of view.***
***	******Zero distortion focal plane.***
**Two surveys in one:**
***	******Photometric survey in 5 bands.***
***	******Spectroscopic redshift survey.***
**Huge CCD Mosaic**
***	******30 CCDs  2K x 2K (imaging)***
***	******22 CCDs  2K x 400 (astrometry)***
**Two high resolution spectrographs**
***	******2 x 320 fibers, with 3 arcsec diameter.***
***	******R=2000 resolution with 4096 pixels.***
***	******Spectral coverage from 3900Å to 9200Å.***
-  **Phase (I) of operations of SDSS is completed in June, 2005.**
-  **Phase (II) will be continuing through June, 2008**.

- www.sdss.org

**Notes:**
SDSS use it’s dedicated telescope at APO, with 3 degree field of view. It is actually two surveys Imaging one quarter of the sky in 5 SDSS bands, and then select candidate for spectroscopy follow up using 640 fiber spectrographs. 
SDSS completed its first phase of operations — SDSS-I — in June, 2005. Over the course of five years, SDSS-I imaged more than 8,000 square degrees of the sky in five bandpasses, detecting nearly 200 million celestial objects, and it measured spectra of more than 675,000 galaxies, 90,000 quasars, and 185,000 stars. For more about the SDSSI, and SDSSII  please see the SDSS web page.

## SDSS & Gravitational lenses and arcs

- QSOs (e.g Oguri)
- Galaxy clusters (see Shin, Hennawi & Makler talks)
- BCGs & LRGs (e.g SLACS Survey, Bolton et al. 2004, 2005, 2006, also see Lin’s talk)
- However, the majority of the multiple-imaging events occur on arcsecond angular scales, requiring subarcsecond resolution for their discovery, for those we need HST + 8-10m spectra

**Notes:**
Several   Gravitational  lenses and arcs surveys    have used the SDSS
images or SDSS spectra to provide 100s  of newly discovered G. arc and G.l. using Galaxy clusters,
QSO lens, LRG.  However  many of these  discovery  relay on HST  + 10m
spectra for object identifications.
SLACS Survey
HST Snapshot Survey of 49 spectroscopically selected  lens-candidates from the SDSS. 
(Bolton et al. 2004, 2005, 2006) 
●   150,000 Luminous Red +MAIN Galaxies from SDSS    (e.g. Eisenstein et al. 2004) 
●   Each galaxy has a SDSS spectrum → redshift(s) & velocity dispersion 
●   Some spectra show higher-z emission lines.    
At least 3 emission lines including OII- 3728 ? →   New lens? 
●   HST-ACS 7-min snapshots in F435W and F814W. 
SELECTION OF LENS CANDIDATES: 
HST Snapshot Survey of 49 spectroscopically selected  lens-candidates from the SDSS.
 (Bolton et al. 2004, 2005, 2006) 
However, the majority of the multiple-imaging events occur on arcsecond angular scales, 
requiring subarcsecond resolution for their discovery, for those we need HST + 8-10m spectra

## The 8 o'clock Arc:Serendipitous discovery in the SDSS Data (April 17, 2006)

- The 8 o'clock Arc:Serendipitous discovery in the SDSS Data (April 17, 2006)

**Notes:**
A year ago, during a visual inspection of SDSS DR4  interacting/merging galaxy pairs catalog, 
unusual pair was found. The central LRG has an  SDSS spectrum which redshift of 0.38. The 
second object is the one above, a blue galaxy, may be a star forming 4arcsec away from the LRG. 
It couldn’t be a galaxy or even two. So I tried the SDSS photometric redshift, it has a redshift of 
.04 which could not be .04 galaxies are larger than. 
That, so if it is not a galaxy, may it is QSO, I tried photometric redshift of QSO ~3. That doesn’t 
look like QSO. The only way that these object looks like an arc is  gravitational lensing.So I used
WFPC2 HST Gravitational Lens Image  Creator, and so it was at 8’Oclok in the eveing.

There are 3 images in the  arc and  a 4th counter  image below the LRG.

## Confirmation APO3.5m SPICAM & 

**Confirmation APO3.5m SPICAM & **
**DIS III (Aug 24, 2006)**

***LBG z=2.73 Lensed *****by LRG z=0.38**
***We have found the Brightest lensed LBG ***
***g=(19.95)> cB58  (g=21.0) Both spectra are similar***
*** ******in UV******  8 O'clock arc is 3xcB58, ***a star forming galaxy (~160 Mo /yr), ***Allam et al (2007)***

- ~11L*

**Notes:**
We had two half nights at APO 3.5m, seeing was 1.0-1.2 arcsec. for imaging we used SPIcam. 
3X300s in gri filters a 15 dithering pattern about the LRG. The fourth image can be seen in 
the g-band even before we do any thing with the images. After normal reduction, images 
were co-added SWARP, and object detection were SExtractor. Slit spectroscopy was 
done using DIS III during the second half of the night. 6exposures were for a total 140 minutes. 
After normal reduction the 6 individual exposures were combined, and the red and blue spectra 
were spliced together. 
The redshift was estimated to be based on measurements of Ly1215.7, Si II 1260.4, I+Si II 
(1302.2+1304.4), C II 1334.5, Si IV 1393.8, Si IV 1402.8, Si II 1526.7,C IV+C IV 1549.5, 
and Al II 1670.8, 
confirming that the arc is indeed a gravitational lens. 
The spectrum of the 8 oユclock arc and, for comparison, the SDSS-measured 
spectrum of cB58, and an LBG composite spectrum from Shapley et al. (2003). 
Both cB58 at and the eight8 oユclock arc at show damped Ly, along with
the typical stellar and interstellar absorption lines found in LBGs, quite similar to those visible in 
the composite spectrum.
However, the "8 O'Clock Arc" is 3 times brighter than cB58, and it is 11L* galaxy, and have high star 
Formation rate 

## Modelling the LRG: 

**Modelling the LRG: **
- -GALFIT (Peng et al. 2002)
- APO3.5 g-band co-added
- image.
- -PSF image using IRAF's.
- -mask out the pixels in the
- arc and counter  image
- to avoid biasing the LRG modelling.
- -LRG model is a
- de Vaucouleurs profile.

*E. Buckley-Geer et al. 2007*
*For more details see Liz’s*
*posters  *

**Notes:**
Modeling the LRG
We used the GALFIT program (Peng et al. 2002, AJ, 124: 266) to model the LRG and  subtract it 
from  the image prior to modeling the lens. We used the g band co-added image since the 4 A4
counter image is clearly seen.  Luckily we have star in the field of view so generate PSF from using
IRAF's  mkobject. We chose to mask  out the pixels in the  arc and counter  
Image to avoid biasing the galaxy modeling. We generated a galaxy model  based on a 
deVaucouleurs profile.

##  Modeling

***Using Gravlens/lensmodel (Keeton 2001) and Singular isothermal ellipse (SIE) ***
*   *

** ****Modeling**

**b****SIE**** = 3.35 ± 0.16"**
**σ = 392 ± 9 km s****-1**
**R****EIN**** = 12.2 ****± 0.6 h****-1 ****kpc**
**M****EIN**** = 1.37 ± 0.13 x10****12**** Msun**
**Mass-to-light ratio = 17.7 M/L**
**Total magnification = 12.3****+15****-3.6**

*E. Buckley-Geer et al. 2007*

*Image plane*

*Source plane*

**Notes:**
Modeling the Lens
   We used the  gravlens/lensmodel  software  (Chris  Keeton astro-ph/0102340) to model the  lens.  
   We  used  the four  image positions obtained by running   SExtractor (Bertin &  Arnout,  1996
   A&AS, 117, 393) on the subtracted image. 
 The LRG position was taken from  the GALFIT  subtraction.  
 We assumed  a singular  isothermal ellipse  (SIE) for the mass  profile of the  lens. 
 We assume a flat  cosmology, ?m=0.3, ??=0.7 H0=100h km s-1.
 Einstein radius= 3.32′′ ± 0.16′′, or 12.1 ± 0.6 h-1 kpc 
 a total mass for the lensing LRG (within the Einstein radius) of 1.35 × 1012 h-1Msun, 
and a magnification factor for the LBG of 12.3. 
The LBG itself is intrinsically quite luminous (~11L*) and shows indications of massive 
recent star formation, perhaps as high as 160 h-1 Msun/yr.

## Lyman-Break Galaxies (LBG)

- z~3, Steidel et al. (1996,1998), Adelberger et al. (1998, 2003) , Giavalisco et al. (1998)

**Notes:**
LBGs are galaxies in which the low-flux region of the spectrum blueward of the Lyα hydrogen 
line at 1216 Å has been redshifted into the U band; 
LBG techniques have been successfully find 1000s at redshit z~3
LBG samples thus provide a vital window into the galaxy populations of the high-redshift (z > 2.7)
 universe (e.g., Steidel et al. 1996,1998, Adelberger et al. 1998, 2003;  Giavalisco et al. 1998).
LBGs resemble present-day star-forming galaxies, 
with spectra characterized by a blue ultraviolet continuum with moderate dust extinction, 
strong interstellar absorption, P Cygni C IV and N V lines from massive stars, 
and weak Lyα emission .

## What is the nature of LBGs? The HDF-N HST + WFPC2 & NICMOS-3

- LBG 3<z<6

- LBG 2<z<3
- Slide from Chris O’Dea

**Notes:**

Q. What is the link between LBGs and the local populations?
Q. Are LBGs small sub-galactic systems that will merge to form more massive galaxies, as predicted by hierarchical cosmologies (CDM)?
Q. What is their mass distribution?
Regardless, their stars must be old

Q. Can they be the progenitors of the spheroids?
Q. What is their metallicity?
Q. What are their stellar mass and age? 

L* corresponds to R ~24.5; Steidel et al. (1999) 
LBGs, however, are generally rather faint, 
and detailed studies of these high-redshift galaxies profit from the additional magnification 
provided by strong lensing.

- MS1512-cB58 (Yee et al. 1996) z=2.73, lensed by foreground cluster, magnification ~ 30.
- Optical and NIR spectroscopy (Teplitz et al. 2001; Pettini et al. 2000; de Mello et al. 2000). A star forming galaxy with a SFR of ~120 Mo/yr and a metallicity 1/3 of solar.

**HST**

**SDSS**

**Notes:**
1st lensed LBG cB58. Discovered serendipitous in CNOC cluster redshift survey (Yee etal.1996),  
cB58 is exceptionally bright (AB6540= 20.41; Ellingson et al. 1996) for its redshift z = 2.72. 
cB58 is a typical L* LBG magnified by foreground cluster MS 1512+36 at z = 0.37.

UV spectral properties of cB58 are remarkably similar to nearby star-forming galaxies.

cB58 has moderate masses and SFRwith a powerful outflows of IS gas, 
with absorption lines being blueshifted by several hundred kilometres per second from the galaxy's 
systemic velocity. 
Absorbing gas is outflowing at ~ 255 km s-1 at a rate exceeding the star-formation rate, 

and although it covers the entire star-forming region, this shows only that the radius of any shell exceeds 
approx1 kpc; it is not known whether the outflows are collimated and localized to star-forming regions, 
or whether they are galaxy-wide. 
The latter is suggested by the observed decrease in the IGM H i opacity in background quasar 
sightlines that are close in projection to LBGs (within 0.7 Mpc 
co-moving). This may indicate that LBGs drive superwinds at approx600 km s-1 for several 108 yr, 
or it might be a statistical fluctuation since there are few LBG−quasar pairs at the smallest separations.

## Cosmic Eye LBG@z = 3.07 Smail et al (2007)

***LBG z=3.07 Lensed *****by a massive ****cluster **
**MACS J2135.2-0102 z = 0.33, magnification of 28 ± 3,**
- a star forming galaxy (~100 Mo /yr).

- ~1L*

**Notes:**
Using Hubble Space Telescope imaging and Keck spectroscopy, Smail et al  reported the discovery of the COSMIC EYE, an LBG at z=3.07 lensed by a forground massive cluster at z=.33
 magnified by a factor of (∼30), magnitude  r=20.3 slitly brighter than cb58.

HST ACS F606W image of LBG J213512.73-010143 showing the twin arcs (labeled as north, N, and south, S) around a compact source, G1. Arc N has several bright knots with a symmetric appearance, along with a low surface brightness extension to the west that has a different radius of curvature. Arc S has a bright knot at each end, connected by low surface brightness emission. The two arcs are not concentric, and we mark their centers of curvature with crosses. The pairs of dotted lines indicate the alignment of the spectroscopic slits in our Keck LRIS observations. The inset to the upper left displays the same field at a higher contrast, while the inset at the lower left shows a true color SDSS gri image of the source; we indicate the direction to the cluster center.
Combined Keck LRIS spectrum of the two arcs (top) as well as the spectra for the individual arcs, N and S (center). We mark the positions of the absorption features we identify in the spectra, both the strong lines arising from the ISM in the galaxy and the weaker photospheric features (dotted lines). The top axis gives the rest-frame wavelength scale at the systemic redshift of the source. For comparison, we show the composite spectrum of LBGs with Lyα absorption from Shapley et al. (2003); note the broad similarity in the main spectral features—apart from the stronger damping wings of the Lyα line in the lensed LBG. We also show in the inset the NIRSPEC spectrum of the eastern component of S, identifying the Hβ and [O III] λλ4959, 5007 lines, which yield a systemic redshift for the source of z = 3.0743. The flux scale of the inset is the same as the main figure.

## The 8 O'clock Arc:current and future follow-up plans

***S. S. Allam, D. L. Tucker, H. Lin, H.T. Diehl, E. Buckley-Geer, J. Annis, J. A. Frieman, D. Kubik, J. Kubo, V. Scarpine, D. McGinnis, J. Estrada (FNAL), J. Brinchmann (CAUP), A. Shapley, M. Strauss, M. Shin, (Princeton), C. Tremonti (U Arizona), C. Martin (UCSB), A. Baker (Rutgers), D. Lutz (MPE), J. A. Smith (APSU), D. Schneider (PSU), C. Kochanek (OSU), M. Gladders (U Chicago), P. Hall (York), M. Oguri (U Stanford)******, ******as of Jan 2007***

## ~11L* what can we learn? 

- We are currently pursuing a vigorous  ground-based campaign to obtain multi-wavelength (UV, optical, NIR, radio) observations.
- Space-based campaign to high-resolution  optical/NIR (HST  WFPC2 and NICMOS), and  to obtain IRAC  and   MIP  images  and IRS  low resolution spectra (Spitzer)
**cB58 is the only other LBG where such  studies have been possible. **

## UV rest-frame Low-res Spectra

**low-res (3250-7500 ****Å****)  LRIS-B on Keck I  (PIs: Shapley and Steidel) **
**   ****to:**
**study the ionizing radiation escaping **
**  ****the LBG below 912 ****Å**** **
**  ****(rest-frame)**
**probe of interstellar absorption line properties**

*Shapley et al. (2007)*
*Low res spectra*

## UV rest-frame Spectra

**Hi-res ~50 km/s, (3500-8150 ****Å-->****LBG 950-2200 ****Å)**** (MMT, PI:  *****Tremonti*****), (ESI on Keck II  PI:  *****Martin*****), no data due to guider failure  or low signal, (Keck II, PI: *****Shapley*****) to study:-**
**stellar content **
**gas kinematics  and gas-phase metallicity **
**Star formation history, high abundance of alpha elements relative to Fe-peak elements would indicate that the LBG formed most of its stars relatively quickly  (< 1 Gyr). **
**cB58 is the only other LBG where such high-resolution spectroscopic studies have been possible. **

## UV rest-frame

**Deep WFPC2 high-resolution imaging HST  (PI:  Allam) to:-    **
**  ****- improvement of lensing model**
**  ****- investigation of LRG and its environment**
**  ****- improved spatial resolution of the LBG**
**    ****(e.g., evidence of merger activity?)**

## optical rest-frame

**APO3.5 (PI: *****Strauss*****), **
**IRTF images (PI: *****Smith*****) see Smith’s poster**
**Optical morphology for the LBG**
**NIR for the LRG**
**NICMOS imaging (PI: *****Allam*****)**
**high spatial resolution rest-frame optical images **

- Kband & colorJHK

- SEDs of cb58
- Ellingson et al 1996

- SEDs

**Notes:**
SEDs
Comparison of continuous star formation models with the observed SED. The data are corrected for extinction equivalent to E(B - V) = 0.3. The four solid lines represent (from bottom to top): 5, 10, 50, and 500 Myr models. The dashed line is a combination the 10 Myr model (15% by mass) and a 1 Gyr single-burst model (85% by mass). The models are scaled to match the optical data (1200–3000 Å rest).

## Optical rest-frame spectra

**VLT SINFONI NIR IFU (*****PI:  Brinchmann)***** to:**
**measure the strength of [OII]3727********H********, [OIII]4959, 5007, and H******** in order to ****derive metallicities, ionization conditions, dust attenuation, and star formation rates, **
**study the spatially resolved dynamical state of the LBG ****to test for evidence of rotational dynamics and/or the signatures of a major merger****.       **

## NIR/MIR rest-frame

**IRAC & MIP images  and IRS  low res-spectra (Spitzer, PI: *****Allam)***** to:**
**constrain the star formation histories and stellar masses,  **
**estimate the bolometric dust luminosities,   distinguish between starburst and AGN bolometric energetics.   **
**The lensed nature of our target enables a unique probe of the nature of  dust  and star  formation  at high redshift using  IRS, which is simply not possible for typical unlensed UV-selected galaxies at similar redshifts. **
**Observations were awarded for another group**

## CO & radio 

**1.2mm continuum and CO(3-2) line observations using   IRAM 30m and Plateau de Bure ****Interferometer (PIs:  Lutz and Baker) to quantify:-**
**obscured star formation**
**dust temperature**
**molecular gas mass and  CO line width**
**spatially resolved studies of the gas distribution and kinematics.**
**(1) MS1512-cB58 (Baker, Tacconi, et al. 2004a, detected)**
**(2) Westphal-MD11 (Baker, Tacconi, et al. 2004b, not detected)**
**(3) Cosmic Eye (Coppin, Smail, et al. 2007, detected)**
**(4) 8 O'Clock Arc (Baker, Lutz, et al. 2007, detected) **
**@850****μm the 8 o'clock arc 3xcB58, see Baker’s talk today.**

## Search for Bright, High-Redshift, 

**3 newly confirmed SDSS lensed arc  **
**with z=2.0-2.4, *****Lin et al 2007***

- Search for Bright, High-Redshift,
- Gravitationally Lensed Galaxies in SDSS

**Notes:**
Is it really a  rare  occasions,

## and even more and more 

- and even more and more
- see Lin’s talk, Kubik’s poster

## We just started.....

## Karachentsev criterion +   16<=g<=21 

- Only if they satisfy:
- Karachentsev criterion +   16<=g<=21

- Merging galaxies:
-                             X12 <= (a1+a2)/2

- Diameter a1

- Diameter a2

- Diameter  (ai)

- X_{1,2}

- X_{2,i}

- X_{1,i}

- Galaxy 1

- Galaxy 2

- Shapley et al (2003)

## Dependence of UV continuum shape on Lyα equivalent width.

- Shapley et al. 2003:- E(B-V) decreases as a function of increasing Lyα emission.

**Notes:**
Left: Plotted in blue, the composite spectrum of the quartile of galaxies with the strongest Lyα emission and the weakest low-ionization interstellar absorption lines is also significantly bluer in spectral slope than the composite spectrum of the quartile of galaxies with the strongest Lyα absorption and strongest low-ionization interstellar absorption lines, which is plotted in red. Right: The visual difference between the two extreme spectra in the left-hand panel is confirmed by the mean E(B-V) for each of the four Lyα quartiles, which decreases as a function of increasing Lyα emission.

## 1216 Ly

**(Pettini et al 2002)**
**low res **

**Hi res**

**1216 Ly******

- Nesvadba et al. 2006 ApJ,650, 661

- Arc+core Lensed LBG @ z~3.2 by the X-ray Cluster
- 1E 0657-56 @ z =0.3  (Tucker et al. 1998)
-  **magnification of ~20**
-   ...LBG at z~3.2 have a rotation curve like a local galaxy ...

**ACS image **
**F814W**

**Notes:**
The strongly lensed z=3.24 arc+core galaxy behind the z = 0.3 X-ray cluster 1E 0657-56 (Tucker et al. 1998) appears to be different from these well-studied high-redshift gravitational arcs. The high magnification ~20 presents an excellent opportunity to investigate the properties of a z∼3 galaxy at different radii with high physical and spatial resolution.
[O III] λ5007 Position–peak-velocity curve of the core and arc. Data in the core are shown as black dots, triangles indicate the velocities in the arc for different magnifications (20 [red], 50 [blue], 100 [green]). Gray upside-down triangles indicate the digitized rotation curve of NGC 4419 taken from Sofue et al. (2003); the black line shows our best-fit elliptical disk model (for the core only).
Using SPIFFI on the VLT, Nesvadba et al studied the spatially resolved dynamics of LBG z = 3.2 by observing the rest-frame optical emission lines [O III] λ5007 and Hβ. The lensing configuration suggests that the high surface brightness core is the ~ 20 magnified central ∼1 kpc of the galaxy, whereas the fainter arc is the more strongly magnified peripheral region of the same galaxy at about a half-light radius, which otherwise appears to be a typical z ∼ 3 Lyman break galaxy. 
The overall shape of the position-velocity diagram resembles the rotation curves of the inner few kpc of nearby spiral galaxies. For Mscr = 20, our data have a spatial resolution of ∼200 pc in the source plane. The projected velocities vrot rise rapidly to ∼75 km s-1 within radii ∼0.5 kpc from the center and asymptotically reach a velocity of ∼190 km s-1 within the arc, at a projected radius of a few kpc radius. The rotation curve implies a dynamical mass of log Mdyn/Msun ∼ 9.3 within the central kpc and suggests that in this system the equivalent of the mass of a present-day bulge at the same radius was already in place by z ~3. Approximating the circular velocity of the halo by the measured asymptotic velocity of the rotation curve, we estimate a dark matter halo mass of log Mhalo/Msun ∼ 11.7 ± 0.3, in good agreement with large-scale clustering studies of LBGs. The baryonic collapse fraction is low compared to z ∼ 2 actively star-forming BX and low-redshift galaxies, perhaps implying comparatively less gas infall to small radii or efficient feedback. Even more speculatively, the high central mass density might indicate highly dissipative gas collapse in very early stages of galaxy evolution, in approximate agreement with what is expected for "inside-out" galaxy formation models.

## Elliptical galaxy lens galaxies with 

**Elliptical galaxy lens galaxies with **
**achromatic residuals**
**HST resolution: galaxy**

## Inada et al. 2003

**Inada et al. 2003**
**Oguri et al. 2004**
**Inada et al. 2005**
**Sharon et al. 2005**

## FOR J0332-3557 at z=3.773 

- (Cabanac et al. 2005, A&A, 436, 21)

## Sloan Lens ACS (or SLACS) Survey, 

**Sloan Lens ACS (or SLACS) Survey, **
**~ 150 galaxies to hunt for gravitational lenses.**

## Slide 36

## Gravitational lenses and arcsThe 8 o'clock Arc:Serendipitous discovery in the SDSS Data (April 17, 2006)

- Gravitational lenses and arcsThe 8 o'clock Arc:Serendipitous discovery in the SDSS Data (April 17, 2006)

- S. Allam, D.  Tucker, H. Lin, H. Diehl, J. Annis,
- L. Buckley-Geer, for the Fermi-cluster group

## UV rest-frame Spectra

**low-res (3250-7500 ****Å****)  LRIS-B on Keck I (PIs:  Shapley and Steidel) to:**
**study the ionizing radiation escaping the LBG below 912 ****Å**** (rest-frame)**
**probe of interstellar absorption line properties**

***Shapley et al. 2007***

## NIR/MIR rest-frame

**IRAC & MIP images  and IRS  low res-spectra (Spitzer, PI: Allam) to:**
**constrain the star formation  histories  and stellar masses,  **
**estimate the bolometric dust luminosities,   distinguish between starburst and AGN bolometric energetics, and **
**compare the detailed rest-frame mid-IR spectra of dust emission  and absorption  with  known  low-redshift  templates.    **
**The lensed nature of our target enables a unique probe of the nature of  dust  and star  formation  at high redshift using  IRS, which is simply not possible for typical unlensed UV-selected galaxies at similar  redshifts. **

## What can we learn?

**stellar content, gas kinematics, gas-phase metallicity a high abundance of alpha elements relative to Fe-peak elements would indicate that the LBG formed most of its stars relatively quickly   (< 1 Gyr).**
**bolometric  dust luminosities, and  star  formation rates, histories and stellar masses, quantify the mass of molecular  gas and CO line width, spatially resolving gas distribution and study  its kinematics, distinguish between starburst and AGN  bolometric energetics,  and compare the   detailed rest-frame mid-IR spectra of dust emission and absorption with known low-redshift templates.**

## LBGs

- What we know about Lyman break galaxies (LBGs) is similar to that of the Milky Way half a century ago.
- ~1000 have been discovered via color selection (Steidel et al. 2003)
- General propeties have been investigated (Adelberger et al.2003, Steidel et al. 1998, Shapley et al. 2003)

## Slide 42

## Slide 43

## Confirmation APO3.5m SPICAM & DIS III (Aug 24, 2006)

**Confirmation APO3.5m SPICAM & DIS III (Aug 24, 2006)**

***LBG z=2.73 Lensed *****by LRG z=0.38**
***We have found the Brightest lensed LBG g=(19.95)> cB58  (g=21.0) ***
***Both spectra are similar***

##          LRG z=0.38

**         ****LRG z=0.38**

## Slide 46

## Conroy et al 2006-

- fg7

## Pixel Size

-      SDSS
- 0.394arcsec

- HST ACS/WFC
- 0.05arcsec

**Pixel Size**

- HST NICMOS/NIC2
- 0.076arcsec

## The 8 o'clock Arc:Serendipitous discovery in the SDSS Data

- The 8 o'clock Arc:Serendipitous discovery in the SDSS Data

- S. Allam,
- D.  Tucker, H. Lin, H. Diehl, J. Annis,
- L. Buckley-Geer, for the Fermi-cluster group

- Gravitational lensing phenomena fall naturally into two cases: (1) strong lensing, where multiple images of a source are seen, and (2) weak lensing, where thousands of different sources have their shapes slightly warped in a coherent way. Recent theoretical expectations (for a recently popular model) for the dark matter structures covering 100 million light-years are shown here: (Credit: R. Cen, Princeton U.)

- The light can be bent enough so that a background galaxy can sometimes be seen by looking around either side of a massive foreground cluster of galaxies above. This is called "strong lensing." Applying Charge-Coupled Device (CCD) technology to astronomy, the Bell Labs team used a natural "cosmic mirage" seen in a Hubble Space Telescope (HST) image of a remote cluster of hundreds of galaxies to reconstruct a high-resolution image of the dark matter in the cluster. The dark matter image (below) shows how much dark matter is tied to galaxies, and how much is smoothly distributed across the cluster. The mass maps are constructed by measuring how foreground masses deflect the light of a background galaxy. Light feels the gravitational pull of any matter, dark or not, and images of distant galaxies are deflected and distorted in ways which are precisely related to the foreground mass arrangement.

## Shapley et al 

***Shapley et al ***
***2007***
***Low res spectra***

- The majority of the dark matter is distributed broadly and smoothly in the cluster, covering a region on the sky more than 1.6 million light-years across. The mass of the individual cluster galaxies appears as pinnacles on this mountain of dark matter mass. Overall, the dark matter in the cluster outweighs all the stars in the cluster's galaxies by 250 times as shown in the mass contour plot above.

- We know that most of the mass is not attached to the individual galaxies in clusters. Above is a simulation of a case where too much mass is placed in the individual galaxies of a cluster.

## GL what can we learn? 

## What is the nature of LBGs?

##  MS1512-cB58

-  One of the reddest LBG
-  The restframe UV properties overestimates the predicted FIR flux
-  LBGs can account for a small fraction of the FIR background (<20%)

**250 GHz (Baker et al. 2001)**

**350 GHz (van der Werf et al. 2001)**

- Unique window to probe   the lensed galaxy, it mass dark matter content
- Unique window to study high redshifted object that would not be possible without the extra power of the gravitational telescope

**The first lensed LBG, MS1512-cb58, **
**Yee et al (1996) serendipitous discovery **
**during CNOC cluster survey, z~2.72 V=20.5**
**  **

## What is the nature of LBGs?

- What is the link between LBGs and the local populations?
- Are LBGs small sub-galactic systems that will merge to form more massive galaxies, as predicted by hierarchical cosmologies (CDM)?
- What is their mass distribution?
- Regardless, their stars must be old
- Can they be the progenitors of the spheroids?
- What is their metallicity?
- What are their stellar mass and age?

## The need for the SDSS 

- ~1000(s) of high redshift objects may be gravitationally lensed, so we need to examine very large areas of sky.
- Identification of a strong lens system hinges on achromatic nature of lensing, so multi-colour imaging is of enormous value.
- + 10e6 spectra

**Notes:**
The need for the SDSS 
one quorter of the sky is imaged in five color bands which +
10^6 galaxy spectra, + 10^5 of QSO spectra,
the SDSS sample

## We just started.....    

- We just started.....