# SDSS J094533.99 +100950.1 WLQ Review Paper
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* Objects with very weak or almost absent emission lines, most of them are reffered to as **Weak Line Quasars (WLQs). References : (Fan et al. 1999, Shemmer et al. 2009, Diamond-Stanic et al. 2009, Plotkin et al. 2010)**
* A few sources lying relatively close by have been studied in greater detail: **PHL 1811** (z = 0.19; **Leighly et al. 2007**), **PG 1407+265** (z = 0.94; **McDowell et al. 1995**), and **HE 0141- 3932** (z=1.80; Reimers et al. 2005).
* The study of **WLQs optical/UV continuum properties, X-ray and radio emission** shows **no obvious difference** from **typical emission line quasars** and **no apparent similarity to the weak-line BL Lac objects (Shemmer et al. 2009)**.
* **Possibilities so far considered include:**
1. **Dust obscuration** or **ex-treme broad absorption line (BAL) effect**, which is **unlikely** since there are **no signs of the deep and broad absorption** troughs in the spectra **(Anderson et al. 2001, Collinge et al. 2005)**.
2. **The X-ray absorbing column is low compared with BAL QSOs (NH < 5×1022 cm−2, Shemmer et al. 2009)**
3. strong **[C III] and C IV** lines are found in gravitationally amplified quasars **(e.g. Dobrzycki et al. 1999, Wayth et al. 2005)**
4. **Relativistic beaming** is a good explanation for the absence of strong lines in **BL Lac** objects but **WLQs**, in contrast to **BL Lacs,** have **bluer opti- cal/UV continua**, are **radio quiet** and **show no variability or strong polarization** **(Shemmer et al. 2009, Diamond-Stanic et al. 2009)**
5. We use the following equations from **Kong et al.** **(2006)**: to **determine the central black hole mass:**
6. **The lack of strong emission lines (except for Mg II) is likely to be intrinsic, consistent with the conclusion reached by Diamond-Stanic et al. (2009) for other WLQs.**
7. A remark-able property of the **SDSS J094533.99+100950.1** spectrum is the **presence of Low Ionization Lines (LILs)** such as **Mg II**, which are thought to form **close to the accretion disk surface** (see e.g. **Collin-Souffrin et al. 1988**) and the **absence of High Ionization Lines (HILs) such as C IV.**
8. The **narrow component** of **Mg II**, which is thought to **form at larger distances from the nucleus**, is also absent from the spectrum.
9. **PCA** analysis performed on the **optical/UV** emission line properties of **PG QSO (Shang et al. 2003**; see Fig. 10) show that, with **increasing Eddington ratio, the UV Fe II emission (measured around Mg II) decreases3**, **Si III]+C III]** emission **increases**, and the **widths of Mg II and Si III]+C III]** lines **decrease**.

**Explainations :**
1. The formation of an **accretion disk** in an **AGN** is a long time phenomenon, occurring in **millions of years** (the vis-cous timescale in the outer disk, **iemiginowska et al. 1996**).However, when the disk finally approaches a **black hole**, i.e. when the inner radius moves from **∼ 10 − 20RSchw** to ISCO (**Inner Stable Circular Orbit**), the **disk’s luminosity rapidly increases** on a **hundred year timescale** and X-ray emission starts **(Czerny 2006)**.
2. The immediate stage after is the **irradiation** of the outer disk which happens in the light travel time across the re-gion (years). At this stage the **accretion disk continuum ap-pears** already to be typical for an AGN. However, neither the **broad-line region (BLR) nor the narrow-line region (NLR) region, exist.**
3. If our explanation is correct, our WLQ should have no narrow **[OIII] λ5007** emission but its **LIL Hβ** line should have already formed (as has the **Mg II line**).
4. A few stages of quasar life are also predicted by **Hopkins & Hernquist (2009).**
5. The activity is likely to cease through a** “naked” AGN** stage **(Williams et al. 1999, Hawkins 2004)** since when the **accretion rate drops**, the op- tical **disk recedes outward** and the **component of the BLR linked to the disk wind disappears (e.g. Czerny et al. 2004, Elitzur & Ho 2009)**
**BLR possible Formation**
1. Assuming a **disk radius** of **1 pc**, a rise by **ten percent** of the radial distance takes **1000 years**, and at that stage **the low ionization lines forming close to the disk, like Mg II and Hβ appear.**
2. The rise to the height comparable to the radial distance takes a factor **10 times** longer, and only after that time the **highly ionized lines such as C IV ap-pear in the spectrum.**
3. The **narrow emission line components** take longer to form and are **likely to be absent at the initial stages**.
4. A similar argument was used for the explanation of the relative **faintness of the [OIII]** line in GPS quasars which are also thought to be relatively young **(Vink et al. 2006)**.
5. Thus, a **WLQ phase** lasts for about **1000 years**. There are almost **100 quasars** classified as **WLQ** **(Shemmer et al. 2009, Diamond-Stanic et al. 2009, Plotkin et al. 2010)** in the whole sample of ∼ **100 000 SDSS quasars**. However only a fraction of those, including **SDSS J094533.99+100950.1** (this paper), **PG 1407+265 (McDowell et al. 1995)** and **HE 0141- 3932 (Reimers et al. 2005)**, may represent a more **advanced stage** with **partially developed low ionization lines**. Therefore, the **probability** of **observing** this **evolutionary stage** can be estimated as **$10^3$ − $10^4$**. This would indicate that the **typical duration of a quasar’s active phase** is only **∼ $10^6$−$10^7$ years**.